I don't think a total reunification will happen.
If we assume an Allied victory, I feel that camaraderie through shared hardship will lead most of the non-defeated countries to re-unify. The defeated won't have much choice.
If we have an Axis victory, they split the losers up and move on. There will be more fighting later.
To the Best of my Recollection:
ISA definitely sides with Germany. Empire State will fight them no matter what, so Allied. Hollywood, as an Empire State rival, will likely go Axis. This means that Pacifica, which would try to stay neutral, would lean Allied. Same with Arixo. Maritime Provinces might side with Nazis, for some conquest if nothing else. Atlantic Coalition will likely be first on their list. Both could well stay neutral. Dixie will try to stay neutral. Internal politics and all. Lots of volunteers for both sides. Appalachia and Free Colorado will be the same, but leaning Alllied. I think Dixie will end up splitting. The Collective will eventually end up Allied. I want to see a West Chicago Airlift. Ontario, Quebec, and Louisiana all go Allied. Texas seems likely to go Axis, but they won't get along with Mexico, which will go Axis. Wherever Texas goes, Dixie will probably go opposite, but both neutral to start. Otherwise Columbia I'm not sure about, but if they see a chance to reunite the country they'll probably jump in Allied.