Fans have long compared the similarities between SEGA and Capcom's two iconic heroes, Sonic the Hedgehog and Mega Man. Both are blue heroes who fight evil scientists who send wave after wave of robot armies after them, and are frequently shown up by their red-hued allies. We could probably go on, but you get the gist of it; they're similar, but would anyone consider them interchangeable?
As you can see, YouTube user "Megamaniscrazy" did just that with Sonic's 20th anniversary game, Sonic Generations (hey, it's Mega Man's 25th, so why not?). There's less Buster-action than one would expect from the Blue Bombers, but it's overall still pretty amusing. Plus, Zero and Rayman get in on the action as well!
Incidentally, while the models for X and Zero look a little odd here, they do seem to match up rather well to the on-screen proportions they had in the Super NES games, do they not?
You can find more details here, though there doesn't seem to be a downloadable patch yet. Thanks for the tip, KKM!