St Pierre et Miquelon is NOT a part of the Schengen zone, and has its own entry requirements.
Agreed - for an Iran passport holder, one needs the appropriate visa to get into St Pierre et Miquelon as per
https://www.doyouneedvisa.com/visa-requirement/iraq/to/saint-pierre-and-miquelon
The question about a visa for Schengen was more about making it easier to get to France in the first place, as that's a prerequisite to fly out from Paris to St Pierre et Miquelon.
I absolutely would NOT rely upon transiting via France unless you had confirmed in advance it would be accepted.
Also agreed. From the ferries website,
https://www.spm-ferries.fr/en/get-ready-for-your-trip/travel-documents/ they point to
https://france-visas.gouv.fr/en/web/france-visas/visa-wizard#/ to see if you need a visa and I believe it's the same website to make the actual visa application.
Of course a Canadian passport would be enough, but I seriously doubt that this is an efficient route with expired Canadian PR docs etc - especially with a one-way ticket.
It's definitely not efficient. Of course, flying into the US and trying for the land border isn't either, but lots of folks do that successfully because they feel that they have no other choice.
The question is if it's viable.
My impression is that the (French) authorities of St-P-et-M will look very hard at anyone trying to use that département to transit elsewhere.
I think OP could handle this by applying for, and actually being a tourist of St Pierre et Miquelon for a bit, and then at the end of the trip eat the cost of the return ticket and try their luck at the ferries. (Again, not the most efficient way, but if it's the only way..)
(And if any doubt of someone's ability to transit on to Canada, they'll probably check with CBSA or other Canadian authorities).
So then if it's a question of the ferries and how strict they are in checking before allowing you to leave. Now, if they actually call CBSA then I suspect it'd be fine, as this is a PR who has enough docs to prove identity as a PR and who has met the RO (and would still be meeting RO later this summer if i'm understanding correctly). So if given all this information, then CBSA would probably say they'd accept this PR.
So the answer to the question on whether or not this plan is viable seems to depend on if the ferry will act like many airlines and just refuse boarding outright because our PR is missing the right doc or whatnot.
This is not really a viable route in my opinion.
It seems the most we know about this is
https://www.canadavisa.com/canada-immigration-discussion-board/threads/flagpolling-at-st-pierre-and-miquelon.819735/post-10580043 which states that border control seems to be when one exits the ferry, but doesn't say much about what checks the ferry folks themselves do when boarding a ship to leave Canada.
From
https://ircc.canada.ca/english/helpcentre/answer.asp?qnum=1231&top=16 it seems that you can use the same documents to re-enter Canada that you used to leave Canada and enter St Pierre et Miquelon.
And from
https://www.spm-ferries.fr/en/get-ready-for-your-trip/travel-documents/ all that's needed to enter St Pierre et Miquelon from the Canadian side is the Canadian DL or Canadian Photo ID.
Now, a literal and strict reading of both implies that using a Canadian DL/Photo ID to get into Canada shouldn't work if the one entered St Pierre et Miquelon from France originally.
But it's possible that OP might slide through the ferry checks ("Has a valid, unexpired Ontario DL? Okay this person is good to go") and not present an issue until OP is in front of CBSA (at which point OP should be let in).
Sorry I don't have other suggestions. This seems to be an ongoing issue for Iranian passport holders, and frankly I think there should be a warning that PRs on Iranian passports should NOT rely upon getting a PRTD in timely fashion in order to be able to return.
Agreed. Especially so considering this: I tried to reconstruct the timeline from the OP's post in this thread - it seems like OP left around August 2024 and a month or so later got the appointment on Sept 2024 to pick the PR card up in person, so if OP had been able to delay the trip by a couple of months, then OP would have had the PR card in hand before flying out of Canada and would have been able to fly back already long ago.