I was just thinking about if WarioWare is canon to Mario, and, a theory I just thought of is that the Mario characters really are just actors in the Warioware + Rhythm Heaven universe. Wario does acting work for Nintendo's Mario and Wario Land games from time to time, which is why he has a different outfit in those games and why the other characters in these games almost never mingle with the rest of the WarioWare cast. Wario Land games also sometimes appear in 9-Volt's Nintendo themed microgame collections.
(Speaking of 9-Volt's microgames somehow containing Nintendo IPs, either Wario somehow convinced Nintendo to license out their IPs to his tiny indie company, or this universe just doesn't have copyright laws. I'd assume it's the latter since you can rip off as many IPs as you want in WarioWare DIY and sell them, and you'll never get in trouble.)
Furthermore, in this theory, Wario and Waluigi aren't at all friends in real life, just in Nintendo's games, hence why Waluigi never appears in Warioware. It's a bit sad, but that's how it is with actors sometimes. On the other hand, Mario and Wario's rivalry is real to at least some extent (or at least it is from Wario's viewpoint,) as shown in a few particular microgames.