15Best: Guardians Of The Galaxy
Now that Disney has acquired Marvel, there are a plethora of choices for Kingdom Hearts III to explore —the most popular choice would probably be The Avengers— but I think Guardians of the Galaxy would fit in better with Sora, Donald, and Goofy. The trio of protagonists are essentially guardians themselves, and
unlike the Avengers, the Guardians of the Galaxy have anthropomorphic creatures already in their wheelhouse. A talking duck and dog would fit right in with a talking tree and raccoon (maybe Howard the Duck could make an appearance to cement their bond further even further).
The best possible plot would involve Sora's group getting picked up by a bad group of aliens in space with the Guardians rescuing them by accident as they were already in pursuit of the ship. It’s similar to the Birth by Sleep world based on Lilo and Stitch admittedly, but it’s a good draft at least.