You simply need a 2GB SD card and download Project M into the SD card. It's the same as if you were going to download Project M on the Wii. That said, because it is a Wii U rather than a Wii, using a GameCube controller is impossible unless you go out your way and by one of those 3rd party accessories only available online. Thus,
I had to endure and practice using a Wiimote plus nunchuck and perfect the wavedashing technique yet again. Despite that, downloading the mod isn't hard and is free to the public. The download link is
here and instructions are also available depending on whether your Wii, or in this case your Wii U, is hacked or not.