If you mean the new Warner Bros movie that is scheduled to be released in 2015, the cast hasn't been announced yet and it's possible that they haven't even cast the main characters. Work doesn't start until 2013 and the script isn't written yet, though a screenwriter has been chosen, so they may still be deciding.
There have been lots of rumours, of course. Earlier this year it was said that Armie Hammer was going to play Batman. It's true he was chosen for the part in 2007, when there was an earlier plan to make a Justice League movie about Batman (that one had to be cancelled due to strike action and other problems), and it hasn't been ruled out but nothing is confirmed. There was also talk of hiring Joseph Gordon-Levitt but it now seems almost certain that he will not be playing the role.
If you want to keep up to date on this film, a lot of the latest information can be found here.