The movie Oz The Great and Powerful is, like most novels, stories, TV episodes, and movies, almost totally consistent with itself, with very few contradictions. If two parts of a work of fiction seem to contradict themselves, fans can try to find ways to reconcile them and show that they are not really inconsistent.
But if the fans fail and the two story elements seen to be totally inconsistent, then the fans may have to admit that those two parts of the story are not canonical with each other, and thus that the story is not 100 percent canonical with itself.
Thus we can say that Oz The Great and Powerful is almost, but not exactly, 100 percent canonical with itself. But is Oz The Great and Powerful canonical with any other books, movies, etc.?
L. Frank Baum wrote 14 OZ books and many other books set in the same fictional universe. And his official successors wrote many other OZ books over decades. All the OZ books are supposed to be in the same canon. But because of Baum and other OZ writers not making much of an effort for consistency, the various OZ books are not very consistent with other OZ books.
Thus some persons might say that most OZ books are almost 100 percent canonical with themselves, but are of lesser degrees of canonicity with other OZ books. For example book A might be 95 percent conistent and canonical with book B, Book C might be 75 percent consistent and canonical with book D, and so on.
And the same may be said about many other novel and movies series.
Many of the early OZ books have now become public domain in many jurisdictions. It is legal to reprint them and to make movies and TV shows based on them without paying royalties to the heirs of L. Frank Baum.
If the creators of Oz, The Great and Powerful had made a strong effort to make it consistent with early OZ books like The Wonderful Wizard of Oz (1900), The Marvelous Land of OZ (1904), Ozma of OZ (1907), etc. etc., they could have created a one way link of canon. Those early OZ books would have become canon in the fictional universe of Oz, The Great and Powerful, but Oz, The Great and Powerful would not have become canon in the fictional universe of those early OZ books.
But the creators of Oz, The Great and Powerful didn't make such an effort and Oz, The Great and Powerful is not consistent with those early OZ books. Thus those early OZ books are not canon in the fictional universe of Oz, The Great and Powerful and Oz, The Great and Powerful is all alone in its own fictional universe and no other OZ books, or movies are canonical with it. At least until and unless some hypothetical sequel to it is made.