Ok lets clear this up.

The Wii-U is backwards compatible with the Wii but not the Gamecube.

However Gamecube games will be avaiable to download on the Virtual Console.

PS: A Gamecube disc can hold up to 1.2 GB of data so your gonna need a big SD card.

PSS: 1.2GB is probablly gonna be expensivbe to download.