Toriyama did not supervise GT, all he did was to contribute with some basic character designs.
Toriyama did however write the backstory for DBO.
See the difference?
He supervised the production. And no just because he wrote a backstory doesn't make it automatically canon.
1. Prove it.
2. Let's recap. The original author, with all legal rights, writes a continuation of his original story, and it's not canon? Are you serious? Do you even know what canon is?