How is the movie for The Avengers going to work?

I figure that The Hulk, Thor, and Iron Man will be in it because they are all connected in each movie, but i was just wondering how Captain America is going to be part of this new movie seeing as the new movie they made put him in World War 2. And does anyone know which other characters will be in the new Avengers movie? spiderman? (i just looked up spiderman and now they are changing the main actor? thats stupid.) Any of the xmen? (probably not, cuz in the last xmen everyone freaking died. what a stupid ending)