Wow that thread got drowned out fast... instead of bumping it, I'll just take it as a sign that the gods of the forum care not... but maybe people in the actual Wii U threads might.
http://www.neogaf.com/forum/showthread.php?t=501693
In summation: If you're having problems playing Online with AssCreed 3 (IE, it showing there are games, but not being able to connect to any) it may be a port forwarding problem, but since I'm not sure what port, just dumping the Wii U into your router's DMZ is probably the best/safest bet. Not sure if it effects any game besides AssCreed 3... but it might.
(edit) The port for x-box360 is 3074, not sure if it's the same for Wii U, my gamepad is dead so I can't test it right now. DMZ for sure works though if your router has the option.