Anyone can share their experience on travelling aboard during the waiting period for DM through a land PoE by a rental car? Is it legal to travel aboard in this period or will it affect anything of DM?
Short answer:
It is legal to travel abroad while a PR card application is in Secondary Review. Canada does
NOT impose any restriction on a PR's travel abroad pending a PR card application.
However, how traveling abroad might affect the process or the outcome can vary from one individual to another, depending on whether the PR is in compliance with the PR Residency Obligation and otherwise admissible.
Longer Explanation:
I have no personal experience with this.
But your question is easily answered in terms of what the rules are. In contrast, the practical effect of traveling abroad while a PR card application is pending under Secondary Review depends on the individual's particular facts and circumstances.
The overriding rule is that a PR's capacity to travel internationally is NOT governed by Canada BUT rather by the passport the PR carries.
CANADA's Rules regarding PR travel abroad:
Canada does NOT impose any restriction, none at all, on a PR's travel abroad. At any time. Whether the PR has a PR card or not. Whether the PR has a PR card application in process or not.
There are two exceptions. One is the PR Residency Obligation, the requirement that a PR be present in Canada for at least 730 days within any five year time period. The Second is that PRs who are also a refugee may be subject to cessation of refugee status, which would automatically terminate their PR status, if they travel using a home country passport or if they travel to the home country (or in some circumstances, that would be the country they fled).
Thus, a PR who has an application for a new PR card pending, whether in SR or otherwise, can freely travel abroad, so far as the Canadian government has a say, just like any other Canadian PR.
Travel without a valid PR card:
Canada does NOT, not at all, preclude PRs from traveling abroad without a valid PR card. This forum is rife with misguided complaints otherwise. But there is a related restriction: the restriction Canada does impose is that PRs need to present EITHER a valid PR card OR a PR Travel Document in order to board a flight or other commercial transportation destined to Canada. This is NOT a requirement to return to Canada. It is a requirement which restricts who commercial carriers can transport to Canada. And, a PR abroad who can submit evidence of compliance with the PR RO is entitled to a PR Travel Document precisely so the PR can board a flight to return to Canada.
If a PR is able to travel to a Canadian PoE, no PR card or PR TD is necessary to obtain entry into Canada. Thus, for example, a PR abroad who does not have a valid PR card can, as is often discussed in this forum, travel via the U.S. in order to arrive at a land border crossing into Canada. Technically proof of identity AND proof of PR status must be shown at the border, but the PR's passport alone is usually sufficient for this, and passport plus an expired PR card, CoPR, or Canadian identification (drivers license, health card) will often make this process go more smoothly and quickly (all the CBSA officer needs to do is verify the traveler's PR status in their system).
Obviously, at the PoE the PR may be questioned about how much time the PR has been abroad, or present in Canada, during the preceding five years, to determine compliance with the PR RO. Just like any other PR. But of course a PR without a valid PR card is more likely to be so questioned, and similarly a PR flagged as having a PR card application pending in SR.
Potential Practical Impact:
This is more complicated because it varies so widely depending on the particular PR's situation.
For the PR who is well-settled and living permanently in Canada, whose trip abroad while the PR card application is in process has been fairly brief, and who is otherwise quite clearly in compliance with the PR RO, the mere fact of traveling abroad should have NO detrimental impact.
For the PR who applied for a PR card cutting-it-very-close or who otherwise is NOT so clearly in compliance with the PR RO upon arrival at the PoE, there is of course the risk of a negative residency determination then and there, which would trigger being reported and issued a Departure Order. The PR is still entitled to enter Canada. And can appeal. Once an appeal is made the PR can apply for and should be issued a one-year PR card.
There is a potential POSITIVE impact as well. Generally Secondary Review is about more than just compliance with the PR RO, even if the referral to SR was triggered by questions about compliance with the PR RO. But, if IRCC's concern is about PR RO compliance, it appears that a PR's short trip abroad and prompt return can sometimes trigger a decision, a positive decision, on the PR card application. In particular, it appears that sometimes IRCC will refer a PR card application to SR if it is perceived the PR is living abroad, so the exit and prompt return can signal to IRCC the applicant actually is living in Canada. Caveat is that, again, SR is usually about other issues over and above compliance with the PR RO, so only a few might see their re-entry into Canada affect their PRC application positively.
While there are way too many possible variations to attempt outlining much of a sample, in general the more questions there are about the PR's presence in Canada, the more travel abroad could tend to have a negative influence, and the longer the time abroad the more so.