Clone Wars and Rebels are both canon, unless by movie canon you literally mean only stuff that happens in the movies. There are some Rebels easter eggs in Rogue One, but I concede that's still a far cry from actually being part of the movie.
And I don't disagree with
Lightning Lord Rule
that Maul surviving was absolutely fucking retarded. He didn't just have his legs chopped off, that lightsaber cut him in half at about the waist. But if the force can keep Leia from dying to a near miss from a capital class weapon emplacement and several minutes of vacuum and unshielded radiation exposure, I don't see why it couldn't keep a bisected dude alive. That being said, as retarded as his survival was it led to 4 excellent stories (2 in Clone Wars, 2 in Rebels) and 1 decent one (Son of Dathomir which was a graphic novel interpretation of a Clone Wars plotline that was left hanging when Disney pulled the plug on the show). So despite being really dumb, good things came out of him surviving.