I quite like Jon Krasinski, even though I tend to think The Office had aired a couple of seasons more than it ought to have. I thought he was far and away the best thing about It's Complicated: unlike the other actors who played Meryl Streep and Alec Baldwin's theoretically-grown children, he, as an in-law-to-be, was the only one who seemed like a plausible grown-up, while still managing to seem open and easy-going without being boring, which I think is a surprisingly hard sweet spot to get.
All of that said, though, he is not Captain America. I mean, I don't think Chace Crawford is either. But I just think Krasinski is far too much of a relatable, regular guy to take up the shield as Steve Rogers. I think that he's into the running speaks to the body type that's become so popular among young Hollywood actors today: the tall, almost willowy type that looks good in slim-fit suits. Sam Worthington may be the only actor in this particular generation with a real jaw. And he's already overcommitted and in danger of overexposure. We don't need him to be Captain America, too.