Personally I kinda feel like the Civil War storyline is wasted on just a single movie. They could have done a movie from Cap's perspective, a movie from Stark's perspective, and then a culminating movie (perhaps under the Avenger's title) that ultimately resolves the conflict.
I mean what kind of Civil War starts and ends in a single movie? Lame
Well the Civil War arc was already started in Cap 2. Will most likely continue after and through Ultron and culminate in Cap 3.
I think it just provides Marvel a great out for contracts and rollover of talent and characters.