3. Ryan Gosling
Why He Could: He can handle the duality of Bruce Wayne and Batman perfectly; for starters, he's immensely handsome and proved in Crazy, Stupid, Love that he has the "cocky guy in a suit" shtick nailed down pat. He can also play a tortured soul extremely well, as exemplified by his smoldering performance in Drive, which sees him playing an emotionally wounded character who keeps a lot pent up on the inside, reflecting Bruce Wayne's own existential troubles. He's a major draw both critically and commercially, making him a very viable fit indeed.
Why He Won't: There's just one problem holding him back; he doesn't really
sound like Batman. Gosling has a rather high, almost effeminate-sounding voice at times which doesn't really suit itself well to this sort of material. That's why his lack of dialogue in both Drive and Only God Forgives likely worked in his favour for what were both badass roles.