According to an IGN Gamescoop, when you load up the game menu you see 3 slots for the each playable character, but there's also a 4th slot that's blacked out. They speculated that it could be multiplayer, but I think it might by a 4th character, probably Jimmy (Michael's son). If you look at the leaked Max Payne 3 handling.dat, there's a section with "Jimmy Vehicles", and various specialised cars like the APC, Dune, and Winky.