"How it would work" in terms of story and lore is really besides the point... because the standards aren't that high!
Prequels are the most KHsy and would be my choice, but original movies are the most iconic, meanwhile the new ones are actual Disney movies. Most likely KH would use A New Hope but possibly The Force Awakens.
Mandalorian would actually be really cool. It could feel like an episode of the show. If they wanted they could make a crazy original planet for the game, or use the one from the Ahsoka episode.
Coolest use of Marvel would be original worlds based on Spider-Man or X-Men with original character designs. It could be more colorful and creative than adapting any specific cartoon or movies. Anime Green Goblin or Magneto in FF-style armor... yes.
As for movie adaptations, Guardians of the Galaxy would be the best, haven't seen the Thor movies but he's the best Avenger and I'm sure Asgard would be cool enough.
Deadpool must cameo and let you summon him, as he is a mercenary. He's probably a huge KH fan honestly.
Sora should finally get his own armor when he becomes a superhero, with a tranformation sequence. If mechs are gonna be a thing, which looks likely, let us combine mechs into one big one to fight a massive enemy.