Enter one of the following codes at the Mercenaries mode character selection screen 
while choosing a character.

Ada (Assignment Ada)      : Hold RB and press A.
Ada (Separate Ways)       : Hold Y and press A.
Leon (gangster)           : Hold Y + RB and press A.
Leon (jacket)             : Hold Y and press A.
Leon (Resident Evil 2 RPD): Hold RB and press A.