The Pokémon World Tournament is a battle facility introduced in Pokémon Black 2 and White 2. It is organized by the Sinnoh League Champion Cynthia.
It appears that the trainers that you fight here, are trainers you've met on journies to the other reigons. The list of the triners you fight are:
Brock, Lt. Surge, Misty, Erika, Janine, Blaine, Giovanni, Lance, Blue (or Green)
Akuroma (info not yet relaesed in this trainer)