Below is USCIS's official sayings on the re-entry permit. From https://www.uscis.gov/system/files_force/files/form/i-131instr.pdf?download=1
1. Reentry Permit
a. If you are in the United States as a lawful permanent resident or conditional permanent resident, you may apply for a Reentry Permit. You must be physically present in the United States when you file the Reentry Permit application and complete the biometrics services requirement. After filing your application for a Reentry Permit,
USCIS will inform you in writing when to go to your local Application Support Center (ASC) for your biometrics services appointment. (See Item Number 3. Biometrics Services Requirement in the General Requirements section of these Instructions.)
NOTE: A Reentry Permit may be sent to a U.S. Embassy, U.S. Consulate, or DHS office abroad for you to pick up, if you make such a request when you file your application.
With the exception of having to obtain a returning resident visa abroad, a Reentry Permit does not exempt you from compliance with any of the requirements of U.S. immigration laws. If you are in possession of a valid, unexpired Reentry Permit, you will not be deemed to have abandoned your status as a lawful permanent resident or conditional permanent resident based solely on the duration of your absences from the United States while the permit is valid.
An absence from the United States for 1 year or more will generally break the continuity of your required continuous residence for the purpose of naturalization. If you intend to remain outside the United States for 1 year or more, you may be eligible to file Form N-470, Application to Preserve Residence for Naturalization
Purposes. For further information, contact your local USCIS office.
b. Validity of Reentry Permit
(1) Generally, a Reentry Permit issued to a lawful permanent resident is valid for 2 years from the date of
issuance. See 8 CFR section 223.3(a)(1). However, if you have been outside the United States for more than
4 of the last 5 years since becoming a lawful permanent resident, the permit will be limited to 1 year, except
that a permit with a validity of 2 years may be issued to the following:
(a) A lawful permanent resident whose travel is on the order of the U.S. Government, other than an exclusion,
deportation, removal, or rescission order;
(b) A lawful permanent resident employed by a public international organization of which the United States
is a member by treaty or statute; or
(c) A lawful permanent resident who is a professional athlete and regularly competes in the United States and
worldwide.
(2) A Reentry Permit issued to a conditional permanent resident is valid for 2 years from the date of issuance, or
to the date the conditional permanent resident must apply for removal of the conditions on his or her status,
whichever date comes first.
(3) A Reentry Permit may not be extended.
c. A Reentry Permit may not be issued to you if:
(1) You have already been issued such a document, and it is still valid, unless the prior document has been
returned to USCIS or you can demonstrate that it was lost; or
(2) A notice was published in the Federal Register that precludes the issuance of such a document for travel to the
area where you intend to go.
NOTICE to lawful permanent or conditional permanent residents concerning possible abandonment
of status: If you do not obtain a Reentry Permit, lengthy or frequent absences from the United States could
be factors supporting a conclusion that you have abandoned your lawful permanent resident status. If DHS
determines, upon your return to the United States, that you have abandoned your lawful permanent resident
status, you may challenge that determination if you are placed in removal proceedings.
My thoughts on your other questions
4. Would having an expired US immigrant visa(unused if I do not activate green card) on my passport have any impact on the Canadian PR renewal application?
None. Canadian PR renewal only cares about residence obligations in Canada.
5. Would having an expired US immigrant visa(unused if I do not activate green card) on my passport have any impact on the Canadian citizenship application?
None. The intention to reside clause for Canadian citizenship application was removed by Bill C6.
6. Would having a prior US GC(if I activate the green card and give it up later) have any impact on the Canadian PR renewal application?
None. Canadian PR renewal only cares about residence obligations in Canada.
7. Would having a prior US GC(if I activate the green card and give it up later) have any impact on the Canadian citizenship application?
None. The intention to reside clause for Canadian citizenship application was removed by Bill C6.
8. Would having an active US GC(if I successfully obtain single/multiple re-entry permit) have any impact on the Canadian PR renewal application?
None. Canadian PR renewal only cares about residence obligations in Canada.
9. Would having an active US GC(if I successfully obtain single/multiple re-entry permit) have any impact on the Canadian citizenship application?
None. The intention to reside clause for Canadian citizenship application was removed by Bill C6.
10. Finally, any idea if not using my US immigrant visa OR giving up US green card would have any impact on my chances of obtaining another US GC through my wife's spousal sponsorship 4-5 years from now, once we are Canadian citizens hopefully?
Not using US immigrant visa is better than giving up US green card, from the perspective of USCIS to adjudicate your second GC application.
1. Reentry Permit
a. If you are in the United States as a lawful permanent resident or conditional permanent resident, you may apply for a Reentry Permit. You must be physically present in the United States when you file the Reentry Permit application and complete the biometrics services requirement. After filing your application for a Reentry Permit,
USCIS will inform you in writing when to go to your local Application Support Center (ASC) for your biometrics services appointment. (See Item Number 3. Biometrics Services Requirement in the General Requirements section of these Instructions.)
NOTE: A Reentry Permit may be sent to a U.S. Embassy, U.S. Consulate, or DHS office abroad for you to pick up, if you make such a request when you file your application.
With the exception of having to obtain a returning resident visa abroad, a Reentry Permit does not exempt you from compliance with any of the requirements of U.S. immigration laws. If you are in possession of a valid, unexpired Reentry Permit, you will not be deemed to have abandoned your status as a lawful permanent resident or conditional permanent resident based solely on the duration of your absences from the United States while the permit is valid.
An absence from the United States for 1 year or more will generally break the continuity of your required continuous residence for the purpose of naturalization. If you intend to remain outside the United States for 1 year or more, you may be eligible to file Form N-470, Application to Preserve Residence for Naturalization
Purposes. For further information, contact your local USCIS office.
b. Validity of Reentry Permit
(1) Generally, a Reentry Permit issued to a lawful permanent resident is valid for 2 years from the date of
issuance. See 8 CFR section 223.3(a)(1). However, if you have been outside the United States for more than
4 of the last 5 years since becoming a lawful permanent resident, the permit will be limited to 1 year, except
that a permit with a validity of 2 years may be issued to the following:
(a) A lawful permanent resident whose travel is on the order of the U.S. Government, other than an exclusion,
deportation, removal, or rescission order;
(b) A lawful permanent resident employed by a public international organization of which the United States
is a member by treaty or statute; or
(c) A lawful permanent resident who is a professional athlete and regularly competes in the United States and
worldwide.
(2) A Reentry Permit issued to a conditional permanent resident is valid for 2 years from the date of issuance, or
to the date the conditional permanent resident must apply for removal of the conditions on his or her status,
whichever date comes first.
(3) A Reentry Permit may not be extended.
c. A Reentry Permit may not be issued to you if:
(1) You have already been issued such a document, and it is still valid, unless the prior document has been
returned to USCIS or you can demonstrate that it was lost; or
(2) A notice was published in the Federal Register that precludes the issuance of such a document for travel to the
area where you intend to go.
NOTICE to lawful permanent or conditional permanent residents concerning possible abandonment
of status: If you do not obtain a Reentry Permit, lengthy or frequent absences from the United States could
be factors supporting a conclusion that you have abandoned your lawful permanent resident status. If DHS
determines, upon your return to the United States, that you have abandoned your lawful permanent resident
status, you may challenge that determination if you are placed in removal proceedings.
My thoughts on your other questions
4. Would having an expired US immigrant visa(unused if I do not activate green card) on my passport have any impact on the Canadian PR renewal application?
None. Canadian PR renewal only cares about residence obligations in Canada.
5. Would having an expired US immigrant visa(unused if I do not activate green card) on my passport have any impact on the Canadian citizenship application?
None. The intention to reside clause for Canadian citizenship application was removed by Bill C6.
6. Would having a prior US GC(if I activate the green card and give it up later) have any impact on the Canadian PR renewal application?
None. Canadian PR renewal only cares about residence obligations in Canada.
7. Would having a prior US GC(if I activate the green card and give it up later) have any impact on the Canadian citizenship application?
None. The intention to reside clause for Canadian citizenship application was removed by Bill C6.
8. Would having an active US GC(if I successfully obtain single/multiple re-entry permit) have any impact on the Canadian PR renewal application?
None. Canadian PR renewal only cares about residence obligations in Canada.
9. Would having an active US GC(if I successfully obtain single/multiple re-entry permit) have any impact on the Canadian citizenship application?
None. The intention to reside clause for Canadian citizenship application was removed by Bill C6.
10. Finally, any idea if not using my US immigrant visa OR giving up US green card would have any impact on my chances of obtaining another US GC through my wife's spousal sponsorship 4-5 years from now, once we are Canadian citizens hopefully?
Not using US immigrant visa is better than giving up US green card, from the perspective of USCIS to adjudicate your second GC application.