You can not compare a handheld gaming system like the 3DS with a console like Wii U. If you do that it would mean that the PS4 would be a flop like the Vita, the Vita has already some of the biggest Sony IPs and still has low sales.
There seem to many interesting games in the pipeline that could rise the Wii U sales.
Of course a good 3D Mario would help. Mario Galaxy 1+2 are in the top three of the all-time-top-games on ranking sites like gamerankings. But there are other games that are more important for sales:
Smas Bros and Mario Kart are a definitive system seller, a new Zelda, even The Wind Waker Remake will sell many Wii Us too. "Xenoblade 2" will sell to the JRPG-Fans and the new Retro game will probably be astonishing. Bayonetta 2 is another game that will definitely sell a few consoles, other exclusives like Shin Megami Tensai vs. Fire Emblem or Sonic Lost Worlds, The Wonderful 101 will make some people buy the Wii U. The new Mario&Sonic Winter Olympics seems to be exclusive on Wii U and past games sell millions!
There will be no hit-seller that rises the Wii U sales to the roof, but many exclusive Wii U games that will make prople buy the Wii U and rise the sales dramatically.
