All wrestlers
Press Up(2), Down(2), Left, Right, Left, Right, Y(2), X at the main menu. A message will confirm correct code entry. After enabling the code, go to the options screen and save your options. This will keep all wrestlers unlocked if you start your game over.
Bonus arenas
Successfully complete the game in career mode to unlock the Back Lot, Gym, Beach Resort, and Casino arenas in exhibition mode.