The Nintendo E3 webpage is now up and there is a little bit of info there:
"Experience.
Game demos aren’t just for E3 VIPs. You’ll be able to try out four unreleased Wii U games, exclusively at participating Best Buy locations. Stay tuned for details."
See how they said four games? My guesses are Mario, MK, Zelda and... have no clue!
Also, on the left side you`ll see the games that will (probably) make an appearance. So far i got Pikmin 3 and Mario and Luigi Dream Team