Yes, Brian Cranston would make an excellent Lex Luthor. Cranston has showed time and time again that his acting chops are up to snuff, and he has the wide range of acting ability to play a nuanced and deep character like Lex Luthor. I would personally love to see him take the role in Superman/Batman.
Historical knowledge of Superman villains would indicate that Bryan Cranston would not make a good Lex Luther adaptation. Physically, his appearance does not match canonical images of Luther. In personal opinion, I feel like Billy Zane would be best candidate in any adaptation of Lex Luther. He physically resembles Luther, and thanks to his portrayal of Cal in Titanic, he definitely has the persona.