Cranston is Luthor. Don't know when it will get confirmed, but I'd bet money on it.
Why? Well, he's been continually rumored for the role, and people like the idea. He's popular following Breaking Bad. I don't think he'd be a hard actor to get (like Pheonix). He's got great villain presence. And when he was asked about the rumor, he rather cleverly did not deny it but dodged the question with "well people just think that because I'm bald, but they can hire any actor and put a bald cap on him!" That's not a denial, its simply a statement that WB can hire anyone. They can, but they've hired him.
The only potential roadblock here would be if Cranston doesn't want to appear in multiple films, which Lex would almost certainly be required to do.