Thus far, three retailers have stepped up, each with an exclusive multiplayer character:
At this point, such bonuses are only being offered for the PlayStation 3 and Xbox 360 editions. Going by the game's official site, several other stores--Toys R Us, Sears, Kmart, Walmart, Target--have similar (but as-yet-unrevealed) pre-order deals lined up.
Of course, actions speak louder than words and renders. That's why Activision passed over some vignettes of the three known pre-order bonus characters in action: