I use strictly use canons when I play fandoms. For me it's an opportunity to develop a world and characters that I'm already very familiar with so it makes plotting much quicker. For instance I would have thought Harry and Hermione would be a thing so I write to put them together and tweak events in an interesting manner that the author hadn't ventured towards. For me, playing in established worlds with established characters is very entertaining and it's something I do with respect and care. A lot of folks do like to use OCs often as an [insert me] sort of situation which I try to avoid. For me, it's just a delight to take a setting (Iron Man, Pokemon, CSI, Dragon Age etc) and explore more of it.

Many folks don't dig fandoms and even more are uncomfortable playing canons. I get that.

But like other genres in writing or roleplaying, everyone has their likes/dislikes and for me, fandoms have been a great source of thrilling and very rewarding storytelling. Just because it's a fandom, doesn't make it any less creative or "original" than other genre based original RPs, at least in my mind.