Well, I've defeated the Champions League twice and by extension, the rest of the tournament so here is my team that I used:
Volcarona@LifeOrb (was wise glasses and leftovers)
252/252 Spatt Speed
-Quiver Dance/HP Rock for a while
Hydreigon@ChoiceSpecs (experimented with Draco plate and leftovers)
Same as Volcarona
Lucario@Choice Band then in the Champs Focus Sash(?)
Same as Volcarona but Att instead of SpAtt
I lost many more times than I won just because of plain old Hax but you may want to make your pokemon more defensively inclined so you can survive super effective atacks and the occasional critical hit. Accuracy should not be under 90 or 80 (luckily, Fire Blast worked well for me). Oh and remember to use PP Ups on low PP moves.
Pokédex is complete (until October 12th that is).