It will be like current gen. Mostly 720p or less with the odd 1080p game. It's very unlikely the small size Wii U is that much more powerful than PS360. Still thanks to the large 32mb of edram, 720p with all the bells and whistles should be a breeze. Full HD is very demanding.
As for framerate, 30fps for TV + control pad is fine for a lot of games. It's when sitting up close and controlling with a mouse does 60fps really become a must. Still games like COD and Mario games like Mario Galaxy and Mario Kart are 60fps because they require the lowest possible latency.