I do not know the rules for traveling to the U.S. Again, rules about traveling to the U.S. are about what the U.S. authorities require.
Not sure why
@Lex2019 keeps referring you to CBSA. Again, whether you can enter the U.S. is
NOT a Canadian question, not a question for Canadian authorities. It is about what the U.S. authorities require.
If your question is whether the U.S. will allow you to enter based on your status as a Canadian citizen, that still depends on U.S. rules not Canadian, and again
is not a question for CBSA. Without a Canadian passport, what other passport you are carrying, including passport entries showing authorization to enter the U.S., will almost certainly dictate whether you can travel to the U.S. And again, that is about U.S. rules, not a question that can be properly answered by Canadian authorities . . . CBSA or otherwise.
If your question is about applying for Canadian documentation while you are still in the U.S., this too is NOT a CBSA question but, rather, a question for IRCC. Depends on what documentation you are applying for.
If Your Question is About Returning to Canada:
Reminder: What you need to return to Canada is not complicated.
If you plan to fly back to Canada: you will need either a valid Canadian passport or "special authorization" (specifically for Canadian citizens abroad without a Canadian passport who have a flight booked to take place in less than ten days).
Or you can re-enter Canada via land border PoE: AGAIN, and notwithstanding border control rules due to Covid-19, you can re-enter Canada by land, since as a Canadian citizen you have a fundamental right to enter Canada. No special documentation needed to do this, just sufficient proof of identity.
(Note: there are some instances in which IRCC online information states that dual Canadian citizens "can only enter Canada" with a valid Canadian passport or special authorization. This is NOT really true, unless "special authorization" is understood to include getting permission to enter Canada at the PoE upon verification of identity and status. Where it states this on various IRCC webpages this is really about what a dual citizen needs to board commercial transportation headed to Canada, not what a Canadian citizen needs at a PoE in order to be allowed entry itself.)
I will reference and link the IRCC information for Canadian citizens abroad regarding obtaining proof of citizenship, a Canadian passport, or for those with a booked flight in less than ten days, information about obtaining the "special authorization" which will allow a Canadian citizen to board a flight headed to Canada. If you are going to be remaining abroad for a lengthy period of time, and thus have time to go through the procedures for obtaining a Canadian passport from abroad (which for you, without a certificate of citizenship, could be a bit complicated with a high risk for rather lengthy processing times), or you plan to avail yourself of the process for obtaining special authorization, see the information published by IRCC I reference and link below.
But it may make more sense to fly to a city near the Canadian border (such as Detroit or Buffalo), and complete the journey back to Canada across a land border.
Again, the latter is OK. Quarantine restrictions apply, but as long as the Canadian citizen can find a means to travel to a Canadian PoE, the Canadian citizen WILL BE ALLOWED TO ENTER, because a Canadian citizen has a fundamental right to enter (and this is practically true for Canadian PRs as well, except the "right" to enter derives from statute).
LINKS to Relevant IRCC Information:
Some IRCC information online which addresses various aspects of this, including in particular information about applying for proof of citizenship, passports, and special authorization, can be found at the following webpages
Find out if you are eligible for a special authorization to board your flight to Canada, see
https://www.canada.ca/en/immigration-refugees-citizenship/services/visit-canada/dual-canadian-citizens-visit-canada.html#findOut
Get proof of citizenship, see
https://www.canada.ca/en/immigration-refugees-citizenship/services/canadian-citizenship/proof-citizenship.html
Apply for a Canadian citizenship certificate: About the process, see
https://www.canada.ca/en/immigration-refugees-citizenship/services/canadian-citizenship/proof-citizenship/about.html
Coronavirus disease (COVID-19): Citizenship, see
https://www.canada.ca/en/immigration-refugees-citizenship/services/coronavirus-covid19/citizenship.html
Also see
https://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=1100&top=23
Also see links to additional information in the webpages above.
Again, note that in these webpages there are instances in which it states that a citizen needs either a valid Canadian passport or special authorization to enter Canada . . . that is about documenting authorization to enter Canada as needed by travelers flying back to Canada, NOT about what a citizen needs at the PoE. A citizen arriving at a PoE does not need a Canadian passport or special authorization to be allowed into Canada.