We’re getting a little off-topic, but Quebec’s Magdalen Islands in the Gulf of St. Lawrence are kind of out of the way. Iirc, unless you want to fly, the only regular service to it is via ferry from Prince Edward Island, not from anywhere in Quebec. It used to be that going to PEI required its own ferry trip, so driving from Montreal to the Magdalen Islands required driving to New Brunswick, taking a ferry to PEI, then taking another ferry, putting you back in Quebec (though in a remote, out of the way part of it).
To make a contribution to answering my own question, Northern Virginia has the town of Quantico, which would otherwise be some quaint but not really that special old harbor town except for the fact that it’s surrounded on three sides by the Quantico Marine Corps base and the Potomac River on the other side.
To get to the town by car, you have to go to the base gate and tell them you are going to the town and they will usually wave you through (though they may reserve the right to search you). I don’t want to find out what would happen to me if I entered the base saying I was going to the town but then did not go there promptly and tried to go somewhere else on the base - I wouldn’t be surprised if a dozen MP’s would pounce on me.
As for the town, it’s a sort of quasi-WW2 military shore leave paradise type place. Almost all the businesses cater to Marines.
My understanding is that historically France has heavily subsidized the islands in order to maintain their toe hold in the region. Also because of treaties between France and Canada concerning the region’s fisheries, there were big advantages to the island’s fishing industry remaining French. These days I think tourism lured by the whole “go to France without leaving North America” shtick is a major part of their economy, so I doubt they’ll be changing anytime soon.
Basically, these little islands were pawns between France and England during the period when they were fighting for control of what’s now Canada. They were passed between them by treaty a few times. France owns them now and since they fought so hard to keep at least a tiny bit of North America they aren’t about to give them up.
In other words, even if the island residents wanted to join Canada (I have no idea whether they do), France would not let them.