I can't think of anything that I would say will absolutely get 10 million.
Galaxy 2-- perhaps 5-6 million. I still see the first Mario Galaxy on shelves, if people wanted 3-D Mario then Galaxy would have crossed 10 million. It didn't.
Other M: This game will be lucky to get 2 million.
Zelda: The only way this is making 10 million is if this game is the great WM+ action game that many of us Wii owners are waiting for. While this is possible, I wouldn't bet on it (at least until more about the game is revealed).
Wii Vitality: this will either be the next big thing, or fail like Wii Music (only with Nintendo can a game that sells over 2 million be called a failure).
I think a new DK game (such as the DKC games), a WM+ game, or a 'New' 2D game (think 'New Zelda' or 'New Mario 2') would have the potential to make 10 million.