Let's imagine a world in which the Avengers movie is so successful and so popular that audiences can't get enough. So, they just keep making more and more Avengers movies, with different line-ups.
In this fantasy world, YOU are in charge of deciding which characters will star in the movie(s), and YOU also get to decide which actors will play the roles.
You can choose any character who has ever been an Avenger, no matter how awesome or how bitch-assed. 616 or Ultimate versions. WCA, GLA, whatever. But you have to pick an actor or actress to play the character(s) you choose.
Well...I guess you don't have to...I mean, I'm not the boss of you...
"You must be proud, bold, pleasant, resolute,
And now and then stab, as occasion serves."
Edward II: Act 2 Scene 1, by Christopher Marlowe