According to Comic Book Movie on Dec. 7, reports have been going around that two villains are to be cast for "Batman vs. Superman". At this time, Gal Gadot, best known for her role in the "Fast and the Furious" films, has taken the part of the hero character Wonder Woman, but now rumors are going around about Lex Luthor, Metallo, and Doomsday are villains being considered.
Callan Mulvey, who is will be in the upcoming "300: Rise of an Empire", is an actor that's being talked about as a possibility. As the rumors tend to gather focus, there are talks that if there are villains, they will only come from the universe in which Superman exists. Thus there may be no bad guys from Gotham city like Joker or Scarecrow.
One should take this kind of information with a grain of salt though as this is just purely speculation, but as the weeks progress, there seems to be an evolving formation that could lead to the "Justice League" film.