They set themselves up as Warlords/surviving govts as per the rest of the American states.
There really should be communities and post-war states that are mixed American-Canadian since Canada had long been part of the US before the bombs (willingly or not) and survival will be more important than nationality post apocalypse.
Add 210 years and what nationality someone’s ancestors were only probably matters to the Enclave.
Given the number of national rivalries alive and kicking after twice that long in our own timeline, one can only call this a rather optimistic assumption (Especially given that Canada appears to have been violently occupied only a decade or so before the Bombs fell).
In terms of plot hooks, I'd argue that a three-way cycle of struggles between Canada-Canadians, French Canadians and US-Canadians over the non-glowing bits of the Great White North would be far more interesting than a 'Well it was long ago and nobody really cared anyway' approach to things: you could certainly mine some black comedy gold from a scenario in which the US-Canadian border is just as
friendly as the US-Mexican (Especially if Americans from the formerly-United States are smuggling themselves into Canada, looking for a better life, at exactly the same time that Canadians are sneaking into the former USA is search of richer prospects: "The grass is always greener on the other side" makes a pretty good punchline when that green is Fallout Green).