It has been rumoured that the Wii U GamePad could do 3D, and now proof has come in playthroughs of Assassin's Creed III.
Players trying the retail version of the Wii U game have encountered the option to enable the stereoscopy feature in the options, and tweak the strength of the effect from 0 to 10. Unlike the 3DS however, players will need to use 3D glasses to view the effect - perhaps reason why Nintendo has shied away from promoting the feature.