Cemu 2.0 officially supports Pretendo under your network account options in the emulator. Currently the only emulator with this kind of functionality is Cemu. Pretendo supports any client that can interact with Nintendo Network. However, once it is you will be able to use Pretendo simply by running our homebrew patcher on your console.
Pretendo is currently not in a state that is ready for public use. Our goal is to preserve the online functionality of these consoles, to allow players to continue to play their favorite Wii U and 3DS games to their fullest capacity. Pretendo is an open source Nintendo Network replacement that aims to build custom servers for the Wii U and 3DS family of consoles.