User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-4697011-20130302075729/@comment-5946566-20130303121935

^ It's confirmed that you can't play with the WiiU and the 3DS online at the same time, because you need your WiiU running an special free app. So you can't play MH3U on the WiiU while other person is playing online with the 3DS using the WiiU as a "router".

(If this is what you mean).