Wii Fit will be the highest selling game this generation.

[OriGin]

Mario Kart will outsell Brawl for sure... I don't think they will be even close to Wii Fit.

I'd also bet that Mario Kart will outsell Brawl. Maybe not in the first week, but in the long rung :)

 

Also, this doesn't include Wii Sports, but it does include Wii Play