Very hard to answer. With Smash Bros going to 3DS too, the WiiU-version will lose majority of japanese sales. So it seems unlikely. But Smash is a title, that has an incredible attach-ratio. It got 7.7 million on GC, so around every third GC-owner had one. Besides the 3DS it seems good, it releases relatively early in lifetime.
The next candidate is Mario Kart. It sold always strongly, nearly 7 million on GC.
A true Wii Sports 3 could easily make this number. But Nintendo seems unwilling to do that.
If - and that is a big if - Just dance establish itself for next gen on WiiU, it might have a chance.
The last candidate on my list is WiiFitU. Both WiiFit for Wii sold over 20 million. As it was accompinied by expensive hardware, I think it might be possible to convert the customers to WiiU also. And old WiiFit-owners can use their balance-board and reduce costs for this game. So WiiFitU seems most likely to beat 10 million at this point.