Ever since Thanos and Guardians of the Galaxy came into play in the Marvel cinematic universe, a lot of fans have been speculating that we might see a massive team-up of the two worlds in The Avengers 2. If you were hoping that would happen, Joss Whedon has just crushed your dreams. It doesn't look like the Guardians will be included in the sequel. Here's what the director had to say when talking to Bleeding Cool,
We’re following Guardians at Shepperton [Studios, with Avengers 2], but we won’t be swapping cast members. Every movie is its own thing and has to be. Unless I take a lot of peyote and write a very different draft… and I’m not ruling that out.
I think that's a pretty clear statement that he isn't including the Guardians of the Galaxy in the script he's writing. As of right now all we know about the sequel is that the original Avengers team will be back with the addition Quicksilver and Scarlet Witch.
Maybe somewhere down the line in phase three or four the Guardians will team up with some other Marvel characters, it's just not going to be the next Avengers movie, which is fine! In the end both movies are likely to be awesome, and fans will be completely satisfied.