Press the red button on the WiiU (the one with "sync" over it if I remember correctly)
wait a second, a text will appear that says that you have to press the red button on the controller (on the back side).
Wait again.
And it is ready to go.
Thank you.
Man, Rayman Legends is FUN in co-op and we're only 3 levels in!!!
I used the GamePad though - can't wait to try out my Pro controller myself.