I just realized that there's another option for some folks, though perhaps not our OPs.
https://www.hollandamerica.com/en/ca/find-a-cruise/n6a10a/v627 offers a cruise from Montreal to St-P-n-M and back.
Traveling commercially by ship doesn't require an eTA (as these are strictly for air travel only). So for folks who have a visa-exempt passport to Canada, you might be able to travel via a cruise ship like the above. ( (This one probably isn't too different from using the ferry - though if one of them were to give one a harder time about the travel docs requirements, I'd expect it's the cruise ship that would be the tougher one to deal with).
The reason this might work is the on the same basis that the pre-eTA air flight regime worked - back those with visa-exempt passports could just travel to Canada on the strength of the passport alone without requiring any extra documentation or authorization. As eTAs are not required for marine travel, it seems that this would still be the case for someone has a visa-exempt passport who flies to a country in the Caribbean or Europe and then boards a cruise ship to a port in Canada.
I looked to see if there were other, sooner options than the above.
I couldn't find any, though honourable mentions go to
https://www.cruisecritic.com/find-a...tinerary&vendorId=18&src=findACruiseItinerary
(This is a cruise from Schengen (Europe) to Canada.)
https://www.icruise.com/itineraries/19-night-bridgetown-to-halifax-cruise_silver-wind_4-25-2022.html
(This particular one interestingly enough has a stop in Roseau, Dominica. This is interesting because some of the OPs here have Indian and Iranian passports, which can travel visa free to Dominica.)
The one from Iceland is a bit frustrating as it looks like it might be workable if you get off at a Canadian port before the ship leaves to Boston (as similarly suggested in
https://travel.stackexchange.com/questions/52299/is-it-possible-to-skip-some-legs-of-a-cruise ). But in practice the cruise line will almost certainly want to see that you have a valid visa or esta to the USA before letting you board, even if you don't use it. (Apparently as per
https://boards.cruisecritic.com/topic/2851077-disembarking-2-days-early/ it's because the cruise ship might not be able to land at a port in-between due to things like bad weather, so they want to make sure that the travelers can get off at the final port.)
Of course, most nationalities that have visa-exempt access to Canada likely have it for the USA as well (though exceptions do exist, such as Emirati citizens (United Arab Emirates) or those who solely hold the obscure British National (Overseas) passport). And if you could do this, you could also just fly into the USA and do the land crossing.
Still, this might be useful info for those individuals who hold Canadian PR and manage to get stuck overseas without their PR card or a valid PRTD, and who otherwise can't make use of the USA option (e.g. for example someone who got caught overstaying in the USA in the past and is subject to a ban there).
Just keep an eye out on the cruise lines and hope that a Canada-Europe line opens up someday without any USA stops. A South America or Caribbean to Canada line without US stops seems unlikely to me, simply because the USA is in-between and makes too useful a refueling and restocking point. That said, other folks on a different forum are hopeful for a direct Halifax-Bermuda cruise someday,
https://boards.cruisecritic.com/top...-controversial-ports/page/3/#comment-68625717