They need an actor who could work well with and look good next to Cavill's Superman.
Should they cast younger or older for the reboot?
Armie Hammer was going to be Bruce Wayne/Batman in the JL film that got shelved when the Hollywood writers strike hit. I still think he'd make a good one, but since he's now The Lone Ranger I'm not sure how viable a choice he'd be. But he's the right age, has the right look, and is a good actor.