How does it work geographically to merge the two characters' worlds? Aren't Gotham City and Metropolis symbolic substitutions for the same space (i.e. New York City)?
I think Cavill can definitely bulk up for the role. He was pretty buff already in "The Tudors," and I doubt that was a major requirement of that role (other than the actor wanting to look good for the nude scenes).
He's a good choice, I think. I'm marginally interested in the film again...