Given Nintendo's dominance on the Wii, there isn't much they couldn't turn into a 10 million seller if they had colossal marketing campaigns. But even Ninty has a budget so doubtful they'll do that for all of their releases.
I'm guessing that Zelda Wii, next Wii series game, and Super Mario Galaxy 2 all have a pretty good shot at hitting that 10 million mark. Of course still got Wii Fit Plus to cross and then Brawl still has a chance as well so might have a couple of more in those.