Colin Morgan. Come on. It's obvious. What has he really been doing since Merlin other than preparing for J.K. to announce a new Harry Potter film and sitting by his phone waiting for his agent to call about it? Let's look at the evidence objectively. He's already played probably the most famous wizard ever, and he played the hell out of it. He's clearly got some experience with magic, and is no stranger to the fantasy genre. More importantly that that, he has an otherworldly quality to him (especially when he played Ariel in The Tempest at the Globe last year), and that would probably be a major asset to this role. He may not have a ton of name recognition, but his face is immediately familiar, especially to the target demographic of this movie.