Heres one of my favourite apps for the Nintendo Wii Homebrew Channel and also available for the WiiU via Virtual Wii, heres whats new in the latest release that lets you play Gamecube Games on the Wii/WiiU:

-Works on Wii and vWii on Wii U
-Full speed loading from an USB device, or a SD card
-Loads 1:1 and compressed .ISO disc images
-Loads games as extracted files (FST)
-Play retail discs (Wii only)
-Play backups from writable DVD media (Old Wii only)
-Memory card emulation
-Use real memory card (Wii only)
-GBA-Link cable (Wii only)
-Play audio via disc audio streaming
-Bluetooth controller support (Classic Controller (Pro), Wii U Pro Controller)
-HID controller support via USB
-Custom button layout when using HID controllers
-Cheat code support
-WiiRd (Wii only)
-Changeable configuration of various settings
-Reset/Power off via button combo (R + Z + Start) (R + Z + B + D-Pad Down)
-Advanced video mode patching, force progressive and force 16:9 widescreen
-Auto boot from loader
-Disc switching
-Allow use of the Nintendo GameCube Microphone
-Use the official Nintendo GameCube controller adapter

Download Here -->