I'm surprised to see a few US posters suggesting Aussies (the Hemsworth boys, Worthington) for such an All-American hero. I would have thought you'd all be insistent he be played by a Yank? I don't often think that nationality is that important in casting but I can certainly understand why people would want Captain America played by someone with an American passport.
It's called acting for a reason.
Of course, there's also a major double standard because hellfire would reign upon us if an American were to play a Brit in Harry Potter or James Bond.