If a movie violates canon, it should use a different name. If the movie isn't good enough to be made without using a name it doesn't deserve, then it isn't good enough to watch.
Tell that to The Godfather and Wizard of Oz, two movies that are both in just about every top 10 of all time list.
"Canon" only comes into play in sci-fi, video games and comic books, which is one reason those wonderful art forms have such trouble getting taken seriously as art.
Oh, and of course, "canon" also comes into play in religion, which also says a whole lot.