Well, they'd just go broad. All of the Guardians are going to be in Infinity War, etc etc. In real terms you're talking:
Captain America, Iron Man, Winter Soldier, Black Widow, Falcon, War Machine, Black Panther, Vision, Scarlet Witch, Ant-Man, Spider-Man, Doctor Strange, Hulk, Thor, the Guardians (either as a group or individually)...
Point is, if they chose to hinge this game on the core marvel properties that are now part of the MCU there's a very broad cast they can choose from still, plus a few extras if you want to dive into the TV stuff. I didn't even touch on villains there either. So sure it could work.