Hugh Jackman, who is probably most famous for his role as Wolverine, has stated that he would love to appear as Wolverine in The Avengers and/or a Spider-Man film and basically said the studios should suck it up and split the cost. As it currently stands Fox owns X-Men and Fantastic Four, Sony owns Spider-Man, and Marvel (aka, Disney) owns Iron Man, Thor, Captain America, The Avengers, Hulk, etc.. When Collider asked what it would take to get all these heroes on the same film Jackman responded with:
“Mate, I ask the same question. I literally asked the same question the other day to Tom from Marvel who works with all the other studios, he works with Sony and Fox, that’s his job to liaise. I said, ‘Man, can this happen?’ and he goes ‘Look, it’s not gonna be easy because you’re working with different studios and they’re their properties.’ But I believe—maybe I’m optimistic, I understand at Marvel they’ve got The Avengers, they’ve got a lot of big things going on, but at some point I just find it almost impossible that there’s not a way to bring Iron Man, all the Avengers characters, Wolverine, the X-Men characters, Spider-Man, and somehow get them in together.
I don’t see the impediment! I’m like, okay you’ve got three studios, just split it three ways in terms of the cost, and happy days it’s all coming together! I would love to… I’m in for it, I’m totally up for it because I think that would be really exciting for fans across the board.”
I would love for this to happen but it isn't likely. The studios are greedy and they don't want to pay the money involved in bringing the heroes together. This shouldn't be the case, though. After seeing the villains announced for Guardians of the Galaxy and The Avengers 2 (specific villains that involve Fantastic Four and the X-Men), I think it could be possible for at least Fox and Marvel to partner up and share a few characters. Even if it isn't all of them. When you have Hugh Jackman on board it's something to at least be considered, I think.
You can see Jackman as Wolverine once again in The Wolverine which comes out on July 26th.