I tried playing the game with the nunchuk. It says, you have to use the "B" button to fire, but is doesn't work?!?!

What am I doing wrong?

You have to raise the power level first by pulling back on the Wii Remote, hold B when you are happy with the power level and then swing the Wii Remote forwards and release B.

Go to missions, training tutorial 1 and it will tell you how to control it that way. It seems really awkward which is probably why it defaults to Wii Remote only with no motion.

Is it possible to play with the Classic Controller Pro? I can't make it work... ?-)

Classic controller isn't supported.