This thread reads like a Tv Tropes. No idea why, since there's shitton of canon bi characters, even in babby cartoons, though most of them are dykes that appeared to be straight before ending up with a girl.
Off the top of my head: Korra, Asami, Princess Bubblegum, Marceline, Star, Jackie, Enid, Boxman, Professor Venomous, Rad (maybe? Ian said his sexuality is "fluid", whatever it means), probably all gems.
I can't really name any canon homo characters tho, it seems like legbutt characters in cartoons come in two categories: bi & unconfirmed.