Hard to say. On one hand HD games sales are pretty MetaCritic based, and reviews are only so-so. But as one of the few kart racers, and one with some pretty awesome creation tools it will certainly have some legs. 1-1.2 million total WW.
XBL: WiiVault Wii: PM me PSN: WiiVault
PC: AMD Athlon II Quadcore 635 (OC to 4.0ghz) , ATI Radeon 5770 1GB (x2)
MacBook Pro C2D 2.8ghz, 9600m GT 512 iMac: C2D 2.0, X2600XT 256