REMINDER: There are multiple decision points involved when boarding an international flight destined for Canada. The two most relevant ones here are:
-- decision to issue a boarding pass
-- decision to allow the traveler to board the plane
Criteria for these decisions overlap but they are nonetheless separate decisions. Obviously, the traveler needs to be issued a boarding pass (or equivalent) before there is a decision to allow the traveler to board the plane (allowing for some exceptions and that in some situations this can be done concurrently).
Decision to issue a boarding pass:
With exceptions, the decision to issue a boarding pass depends on getting a "
Board" response in the CBSA system, based on API data, including information from the required document, entered into the system. This is an automated decision. Not a decision made by the airline, nor by a Canadian official. But by the machine, so to say, an automated electronic decision.
See CBSA "
Guide for Transporters" for more detailed information about exceptions, link posted below.
That said, the airline still has responsibility over and above this to screen travelers, including to assure their status authorizing entry into Canada. So, being issued a boarding pass does not guarantee the traveler will be allowed to actually board the flight. There are many reasons why boarding might be denied. Here too there is a lot of relevant information in the CBSA "
Guide for Transporters" linked below.
The airlines have other criteria they can and typically will apply before actually issuing the boarding pass. Some so obvious it is taken for granted, like payment and verification of traveler identification, and verification the traveler has the proper travel document(s).
The latter, valid travel documents, usually means a valid passport. In some circumstances, for some travelers, the passport itself is sufficient (visa-exempt passport for individual who has eTA for example; U.S. or Canadian passport for another). For others, additional documents are necessary (for most PRs, a valid passport PLUS a valid PR card or PR TD is necessary, noting that the PR card is NOT a travel document; likewise for Canadian citizen without a Canadian passport, another country passport is insufficient, unless a U.S. passport, and they need to present a special Canadian TD for citizens).
In addition to the FAQ referenced and linked in previous posts,
https://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=1053 which reflects the change just last year, as of April 26, 2022, adding U.S. PRs to the list of those who can board flights to Canada, a more complete PDI with relevant information (plus some) is here:
https://www.canada.ca/en/immigratio.../visit-canada/entry-requirements-country.html
The CBSA guide for transporters is here:
https://www.cbsa-asfc.gc.ca/trans/guide-eng.html
It is lengthy, complex, and does not completely answer the question posed here.
My impression is that a Canadian PR with a valid passport and a valid U.S. Green Card should have no problem boarding a flight to Canada FROM the U.S. even if they do not have a currently valid PR card. Perhaps carry a copy of FAQ and have urls to both the FAQ and the PDI about entry requirements. Whether the other documents showing U.S. PR status, as listed in the FAQ, will work as well, I am less confident but they should.
I would be far more cautious about flying from other countries to Canada. Should work but . . . again, the real world is rife with wrinkles.
I haven't read everyone's input on this thread yet, and there seems to be a really good, in-depth discussion going on. I skimmed and have some thoughts on some of the points and anecdotes raised, but for now, I just want to give an update of what I learned calling some airlines and CBSA.
1. Air Canada on two separate calls (talking to two separate agents) unequivocally confirmed to me that me being a PR does NOT matter. They will board me so long as I can produce a valid passport (whatever country, doesn't matter) and a valid US LPR (green-card).
2. Porter Air was difficult. Called twice. The first agent seemed to have no idea what the requirements are, and insisted I would be denied boarding because I am an Indian citizen (kept going back to that). The second told me they cannot advise on the documents required to board the plane and that I should check with CBSA (seems silly to me, because at the airport the airline does have to make a decision on who to board based on documents provided). When pushed they said whatever the CBSA entry requirements are, the same would apply for boarding, which of-course doesn't help me much.
3. CBSA claimed they could not comment on the documents required to board, that would depend on the airline, and I should check with them. I called twice, one told me I would be granted entry based on my green-card and Indian passport DESPITE being a Canadian PR (which I don't believe is right), the second said CBSA would check if my Canadian PR is valid at the point of entry, and I can present expired PR card / COPR.