So I read that entire wiki page. If you go only by George Lucas, nothing except the films is really canon. Though he also claimed there would never be another movie. So whatever that's worth. The artist in him has a deep conflict with the business side. Considering there's nothing to protect anything labeled C-canon if George Lucas suddenly decides to debunk it, that's really not much to go on.
But the fact he hasn't debunked it means we have to accept it as canon. And were not talking about an obscure EU novel, Darth Bane is a major