I assume you're talking about Loadiine, and if that's the case, no. Not yet, at least. We don't have the ability to connect to a game's online network.
While you cannot access Course World using Cemu or Loadiine GX2, you can download dozens of user-made levels and inject them into your save file. That, unfortunately, is the only way to do it.
Here's a good repo: https://www.reddit.com/r/CemuMarioMaker