Re: some advice for cantering
As a quite inexperienced rider, I can't offer solid advice, but I'd agree with Rio, in the school I'm always seated during canter, as Rio says, for more control and collection.
Out on a hack, I always hover just because we tend to go faster and its easier to keep balance. Plus, if something were to ambush us ( a plastic carrier bag for example...) I'd find it much easier hovering to ride out a spook because you're less in contact with the saddle, and you can keep above all of the turmoil.
It also depends on how long you like to have your stirrups, longer stirrups would give a deeper seat and make it easier to sit during canter, but the short "jockey" style would probably be more suited to hovering. (Obviously not properly like jockey stirrups, but you get my drift haha!)