Topic: Does the WiiU play gamecube games in Wii mode??

And does the adaptor allow me to use GameCube controllers in Wii mode??

No. No. Sorry.

Officially no. And even unofficial, the WiiU can't play GameCube discs.

Out of every single thread on this website, this is the one I want to answer yes to the most

Official no, unofficially no even with gamecube discs, however unofficially without gamecube discs... yes you can, but its not recommended and i'm not going to discuss how to or why here, just do a youtube search on it.

Its a shame the GameCube controller adaptor gathers dust I wish they'd patched in support for at least Mario Kart 8 and Wind Waker HD at least.

@bluemage1989: maybe if Twilight Princess HD gets confirmed it may have GCN controller support. maybe.

Um no cause its called Wii mode not Gamecube mode.

Unofficially you can yes. And yes, it works with the gamecube controller adapter. I was playing Mario Sunshine on mine about an hour ago.
Youtube is a good place to look for info (trust the videos with all the upvotes)