3. Ben Affleck
Why should Affleck join the DCCU? He already has, of course. Batfleck has already collected a warehouse full of derision and negative reaction, but it goes along with all of the hate for the other casting choices and the DC Universe as a whole. Affleck could nail the role, and if he does then he'll likely be appearing as Batman again and again. His directing career has also taken off, though, and his films have all been acclaimed. Argo, his most recent, earned a Best Picture Oscar, and so Affleck is in high demand as a director and an actor. His next project, the Dennis Lehane adaptation Live By Night, has been pushed back due to Affleck's commitments to Batman.
What should Affleck direct? If Affleck's going to direct anything under the DC umbrella, it's more than likely a movie that he'd also be starring in. That leaves Batman solo films and any future team-up/Justice League films in the post-Snyder era.