FIFA 13 is Wii U eShop's first demo
There is one game demo on the Wii U eShop in North America, and it's for EA Sports' FIFA 13. The approximately 1.2GB download is available within the game's page on the eShop, though the size isn't explicitly shown until you begin the process.
Bear in mind that there is no dedicated section for demos in the store, nor is there a way to search for demos. Instead, you either have to click on individual game icons to see if demos are available, or view everything in the eShop as a list and hunt for the "demo" icon.
Having just done all that, we can confirm that FIFA 13 is at present the only demo.
[Thanks, Jon B.]
