Armin ShimermanWhy he should be cast: Much like Patrick Warburton and Brandon Molale, he has a big fan following pushing for him to get cast. He looks the role.
Why he should not get cast: He might not be a big enough "name" star for such a featured role in a major motion picture.
Conclusion: He might get an interview, but might not make it to a screen test.
Why he should be cast: He is a big "name" and probably the only actor who is Sivana's height. When he's not in an outlandish hairpiece, he looks just like Sivana. A great talent.
Why he should not get cast: At age 71, he's a little too old for the role. Also, I don't think I've ever seen him in a role where he doesn't have his New York accent, which doesn't suit Sivana.
Conclusion: If this were 2004 or earlier, he'd be the front runner.
Why he should be cast: A huge movie star and great actor that would bring a magnitude of star power and legitimacy to the film.
Why he should not get cast: At age 77, he's older than Pesci.
Conclusion: Despite his age, I think the studio will give him serious consideration.
Why he should be cast: A good actor, and would bring humor to the role, echoing more the Fawcett Comics version of Sivana.
Why he should not get cast: Concern he may not be able to make Sivana dangerous enough.
Conclusion: He will be given serious consideration.
Why he should be cast: A great actor and looks the part.
Why he should not get cast: He played the Mandarin in "Iron Man 3", in an outside the box comedic take that has left serious bad blood with the fanboys.
Conclusion: If this were pre-Iron Man 3, he would be considered. Now, however, not likely.
John MalkovichWhy he should be cast: A good pick if they were going with the New52 version of Sivana, who starts out tall, and becomes troll like after being exposed to magic.
Why he should not get cast: While its possible the movie may adapt one or two concepts from the New52, it won't be a complete adaption. The New52 Sivana would have to be nearly all CGI post his transformation, and may look too fake or silly.
Conclusion: Little to no chance of being cast.
Jackie Earle HaleyWhy he should be cast: A good actor who has done respected work in the genre. He looks the role. Is the right height and age. Bonus points for being in an episode of the 1970s Filmation "Shazam!" TV series in his teen idol days.
Why he should not get cast: No valid reason.
Conclusion: He's the definite front runner, and, I'll say it, he should be cast in the role.