It is going to be a real close race between Xbox360 and the Wii.
The Wii suffers from having lots of games with long legs. Mario Kart, Brawl, Wii fit, and Galaxy will all sell consistently well over the Wii's lifetime. This will allow for less money for other titles, which could in turn keep them from the 1 million mark.
On the other hand the Wii is heading towards the largest fanbase of any console, which means that a game doesn't need as much to reach 1 million.
Xbox 350 already has a good sized lead. Sports games reaching 1 million is pretty much guaranteed. Also the Xbox 360 has a good attach rating.
It is going to be close between those 2 but I think 360 will win out but just barely. If you were asking about 3, 5, 7, or 10 million sellers than it would be the Wii easily.