There was enormous draft resistance (violent rioting, put down with troops) in Quebec, during the Second World War. Suppose a fascistic Quebecois leader arose, and got himself elected Premier of Quebec? While its certain Quebec would not have been permitted to withdraw from Canada during the war, perhaps shortly afterwards Quebec would be granted national independence, and with Canada cleaved in two, her provinces might well have joined the Union (perhaps with an Ontario-rump Canada persisting). I don't see any real way for any two U.S. states to remain outside such a Union, other than with regard to Alaska and Hawaii retaining Territorial status (although I don't think that really counts; they'd still presumably be part of the same nation, just with a lesser status). Puerto Rican nationalists nearly assassinated President Truman around this time, and also shot (non-fatally) half a dozen members of Congress on the House floor, so perhaps Puerto Rico would have been granted independce along with Quebec.
In a North American Federation minus a Quebec allied with Franco's Spain, Salazar's Portugal, and other rightist states, and a Puerto Rican nation associated with terrorism, it seems likely anti-Catholic sentiment would have been slightly higher in this nation, and thus a Kennedy Presidency would probably never have occurred.
Once at a used book store, I came across a tome authored shortly after the Second World War, entitled Union With Britain Now!, the cover of which showed a map where the USA, Canada, Britain, the Irish Free State, South Africa, Rhodesia (all the way up to the present day Kenyan-Ethiopian border), Australia, New Zealand, Jamaica, British Honduras, and a few other locales (the Falklands, Cyprus, Malaya, etc.) were all one nation (India/Pakistan/Bangladesh probably wasn't included, although Sri Lanka-then-Ceylon may have been). I really wish I had bought that book, alas.