It has been revealed that the Pokémon to be distributed at all screenings of both 14th Pokémon movies are Reshiram and Zekrom. However, differently from how previous Pokémon were distributed to games, this time, the Pokémon a player will receive is dependent on which game they use to download it. Players of Pokémon Black will receive Zekrom, and those who have Pokémon White will receive Reshiram; one will receive the Pokémon which would be unobtainable to them in-game.
Source(s):
Pokémon Series Official