I'm having a hard time believing that the military would stage a coup in such a situation unless they had promises from at least the American government that their new facist government would be recognized. I feel like any leaders trying to impose top-down ideological change are going to think about things like how ideological change will affect foreign relations before they act. Bottom-up ideological change (i.e. a revolution) on the other hand tends not be as good at planning ahead, which is why I feel that war with the USA is more likely to occur under this scenario.
On the other hand, maybe the facist coup does occur with promises of nonintervention from a conservative US president, who then is ousted in the next election and replaced with someone who is more anti-facist and supports intervention in Canada.
I could definitely see Ontario and Quebec going their separate ways, and to a certain extent BC as well, but I can't see either the prairie provinces or the Maritimes (there were not "Atlantic" provinces at this time because Newfoundland didn't join Canada until 1949) trying to go it on their own. This would be happening during an era where free trade is far from guaranteed, and the prairie provinces would need a guaranteed market for their grain. IMHO, BC and the prairies are more likely to stick together than fall apart, as BC's ports are useless without connection to the hinterland, while the prairies need a port through which to export their grain (Churchill, Manitoba just won't cut it). Similarly, the Maritimes, while they have some resources such as fish, pulpwood, coal, and potatoes are really dependent on having a hinterland connected to their ports. If Ontario and Quebec want to go their separate ways, they'll either petition to join the US or try to get Britain to take them under its wing again (this scenario could be plausible if Britain wants to use Halifax as a military base in North America in case of future uprisings).