Pokemon X/Y has the best chance at it. All it needs to do is sell a wee bit better than Black/White lifetime. I can easily imagine X/Y selling 20 million total.
Besides that... Super Mario 3D Land has a good shot, though it certainly won't break 20 million. Mario Kart 7 should make it to about 20 million at least assuming nothing goes terribly wrong down the line. New Super Mario Bros 2 is underperforming compared to its predecessor by about 40%, but even this should leave it with well over 15 million.
As for everything else... Pokemon G3 remakes probably will "only" sell 10 million. G7, if it comes out for the 3DS, will likely perform far worse than G6. Like Ruby/Sapphire remakes, Animal Crossing is simply never going to shift much more than 10 million. Besides that, the only candidate for a megahit left on the 3DS, based on worldwide popularity, would be Mario Party: Island Tour, if it turns out to be something special. Which it probably won't, considering the lack of online play.
So, in short:
1. Pokemon X/Y (20 million)
2. Super Mario 3D Land (18 million)
3. Mario Kart 7 (20 million)
4. New Super Mario Bros 2 (17 million)
Four is not a lot, but that's still far more than most platforms get.







