According to MTV news, the actor voicing Metallo will be John C. McGinley who also starred in such animated features as "Clone High," "Spider-Man: The New Animated Series," "Justice League Unlimited," "The Boondocks," etc.
John is pretty excited about his portrayal because as a father, his children will be able to get a glimpse of dad in an animated release. "My son is old enough to hear and recognize my voice coming out of the characters, but it doesn't resonate with him yet," McGinley said. "My daughter will, and that is pretty cool. Not necessarily to be a killer robot, but we will see how things evolve."
With Metallo being featured in "Smallville," played by Brian Austin Green, it'll be interesting to see the representation McGinley can bring to the animated feature being released on September 29th.
I feel a good voice actor/actress can truly bring out a character so I'm waiting to see how Metallo comes across vocally through McGinley.