Indeed, proper "canon" depends on the company employing the term. As Moka mentioned, Disney canon is determined by its list of animated theatrical releases. With Star Wars (for example) anything from the movies, paperback novels, etc is considered canon. In that case, you can have a random author working on a Star Wars novel who introduces new characters/ events that are then considered canon. Why George Lucas does that to us, I don't know...its hard to keep track
One last example is Games Workshop. They produce a fantasy game called Warhammer. Anything that it produces in rulebooks and armybooks is considered canon but the novels its sister-company releases is NOT considered canon.
In a word, to each his/her own.
Unless we can get a Disney historian or some official to tell us what is and is not canon, then I think we can debate until we are blue in the face. Of course, the ruling Moka provided can fill in the gap as well
In my own personal opinion, I consider the movies canon and that's it. I don't take any other characters into consideration. Keeps it easy for me...
Cheers.