I don't think you can. I believe they just choose random characters.
Higher your level harder your opponent, that is how it goes.
Trading my Wii again! Come on home 360!
Games: Metroid Prime 3, Super Paper Mario, Ghost Squad, Link's Crossbow Training + Wii Zapper, Geometry Wars, Battalion Wars 2
man that sucks, but if its random then its possible that someday ill fight one of my miis right?
Depends on the sport. I've never fought one of my miis in boxing, but I usually see all of them during baseball.
~Well, it's been the ruin of many a poor boy and God, I know I'm one ~
i really wanted to box the $#!t out of my teachers(miiis) :P