This is assuming that:
-It releases in 2016, for only the Wii U
-It is as well recieved as the other 3D Zelda's (Which average at about 96/100)
Edit: If you're wondering why there is talk about Skyward Sword, the orignal thread title was whether it could outsell Skyward Sword. But I did not know that that game was hugely undertracked at VGC, so I changed the title (And it is 4 million because Zelda U would need about 4 million to beat VGC's number of Skyward Sword).
Can't wait for The Zelder Scrolls 3: Breath of The Wild Hunt!