Not very easy as the 3ds but it is still possible

Yeah. If you can mod a 3DS, you can mod a Wii U. wiiu.hacks.guide is your friend.

Honestly I found modding the Wii U and vWii easier than modding the 3DS. But maybe it's cause 3DS was the first thing i modded

The wiiu modding is easy if you follow the wiiu guide but you do want to backup your nand first

It's really easy. Just follow the guide and your good to go. Plus, Pretendo has way more features on the hacked version.