This is an indefinite stalemate. Both characters can fly, heal instantly, extreme durability and strength, neither can be BFR'd, and neither can be killed.
All other powers aside; if both guys have flight and immortality, then neither could ever lose. And both guys here, for all intents and purposes, are immortal.
The only way I can see either guy winning is if Marvel-Guy manages to deep freeze DC-Guy(which Plastic Man is particularly vulnerable to) and shatters him for at least a ten count, or if DC-Guy can manage to KO Marvel-Guy, which I think would be extremely difficult - albeit not impossible - considering part of the amalgam is Hulk with an adamantium skull.