Coming from EA's website...

If you sign up to play EA games through a Nintendo Wii U console, your Nintendo account information will be provided to EA so that we can establish an Origin Account for you. You need an Origin Account to play EA’s titles online. By signing up to play EA’s titles, you agree that limited user account information can be transferred to EA. Information transferred to EA includes your Mii information, email address, Nintendo Network ID, friend list, country, language and date of birth but does not include credit card number or other financial account information.

Well isn't that rather telling! Now we know a little bit more of what goes into playing the Wii U online. You'll have a Nintendo Network ID and online friend list. You'll also have an Origin account created for you when playing EA games. Thanks to Jonathan for the heads up!