Darth Mauls return is the moment I've been waiting for but the ways you mentioned I don't see as possible. At the end of the Clone Wars Maul was defeated by Sidious who said he wasn't going to kill him because he had plans for him. Unless Maul could over power Sidious, Vader and the entire Galactic Empire he has zero free will and is completely under Sidous's control. With this being said that is why i think the theory of him being the head Inquizitor would be cool and I'm behind on Rebles but I know in S02E01 Sidious said to dispatch the next Inquizitor which I instantly thought that would be how Maul would come in.
Maul is let escape by Sidious in a plan to flush out mother talzin in a clone wars special 4 part mini series At the end talzin ssacrifices herself so maul can escape while she fights Sidious Dooku and Greivous kills her So maul is on the run already so could appear in Rebels and yes it is canon
I definitely feel blessed that you guys would share this - a million thanks and for everyone watching- much love from Dash #MTFBWY