And there is always Russell Crowe who wasn't bad in The Quick and the Dead. Brad Pitt would be the obvious choice or possibly the Wahlbergs as the Earps. Johnny Depp could fit in (and was already in a Western). Granted, they'll try Ben Affleck as a Sheriff or something and it'll flop.

The problem isn't with the actors. It's just that nobody thinks to make Westerns anymore (or can get the funding).