You can see how you'll create your Miis on Wii U by checking out these screenshots of the Wii U Mii Studio.
These screenshots from the Nintendo Japan website show what the Mii Studio will look like in Japan. As on Wii and DS, you can choose from loads of facial features, picking your nose (not literally picking your nose. That would be disgusting), eyes, eyebrows and so on.
If you can't be bothered with that, it looks like you'll be able to take a photo of your face with the Wii U camera and a Mii will be generated for you. Just like on 3DS. The screenshots also show a QR code which are handy for sharing Miis.
Do you like the look of the Mii Studio?