How about a slightly different plot that's a bit less random? How about the Galactic Empire... or perhaps the Sith Empire found a wormhole leading into Earth space. They immediately set out to conquer it while rebels and Jedi types land and offer aid to those upon the Earth.

Now that I'm spinning. How about the Empire, Sith or Galactic, discover an ancient alien artifact. The item is just like a giant stargate, mass relay or some other transportation device left over from when the Earth was colonized by ancients.from the Star Wars galaxy many centuries before.

This leaves opportunity for the Marvel characters to possibly disable the artifact or perhaps smuggle themselves through this portal and take on the Empire's leaders directly or perform some other clandestine feat of daring do.