I've tried to understand how they function but it never seems consistent. What determines the nation they pick to lead the union? And are there pan-nationalism outside of Europe like East-Asian pan nationalists?
Nope. You can get it as a secondary power.I think it has to do with GP status.
Gran Colombia and USCA are not cultural unions but the USA is. I would say that Pan nationalists spawn for anyone with an on map cultural union but I've seen someone post about Arab pan-nationalists.I think Gran Colombia and USCA might have pan nationalists, but I'm not sure. The USA also has pan-Nationalists for some silly reason.