I'll say again, if stage = character, then where's our Nintendog fighter?
Would it be a Labrador Retriever like Brawl's AT? With it's Final Smash being what it does in Brawl?
Would it be a cat? (Maybe a Nintendogs + Cats version of Sakurai's Cat?)
Would it be one of the toys, since the characters are the size of toys in the Nintendogs stage? The Talking Bird, perhaps? Or even the Stuffed Dog? Who wouldn't want to play as a stuffed animal come to life? And if it was the Stuffed Dog, then no one would feel bad about beating up actual puppies or kittens.
After all, Sakurai changed his mind on the Villager, and Nintendogs IS a major series for Nintendo....