While I realize a few of these actors tend to be put in fan casts for a Justice League movie, I think they’re near perfect choices for these characters.
I'm making this post because I'm excited to see a cinematic universe for DC so ideally, Cavill is Superman in this lineup.
Jim Caviezel would be different enough to reintroduce Batman without having to be repetitive of Bale. I think he resembles the Tim Sale version.
Gemma Arterton as Wonder Woman because she has a natural beauty to her, like an Amazon. She looks just like the New Frontier incarnation, which is what I think Diana should be.
Carl Lumbly as Martian Manhunter not only because he voiced him in the show but because I’ve been watching Alias a lot lately and think he could pull the character off easily.
Bradley Cooper as the Barry Allen Flash because he already evokes that character in almost every role he chooses.
And finally Idris Elba as the John Stewart Green Lantern because he’s a way to ignore the Reynolds movie from a few years ago (and he also fits the part). If he brought in a similar energy to what he has in Luther, it could be something special for a superhero film.
As for a villain, it might be fitting to bring it back to Superman since he is the prime member of the Justice League. If there was one thing that Avengers missed, it was making Cap stand out as a leader. While that made sense in the story's circumstances since he had just woken up into today's world, it was still something that the movie didn't have. Bringing in a Superman villain would make Clark take charge of the situation, giving him the role of a leader.
That is why I suggest Paul McGann as Vril Dox AKA Brainiac. I think he has the right look for the part.