Board Thread:Naruto News/@comment-2156952-20150115130338/@comment-3279282-20150119231808

Well, canon is normally defined as anything that is included in the main story. Kakashi Gaiden is canon, for example. Anything that expands from the main story is not canon, for example movies, side stories and filler.

As least that's how I understand it. What the author says about it is not that relevant. The tenth movie isn't canon because Kishimoto said so, but because it's included in the main story as chapter 699.5 and the events in the movie are part of the plot (same as Kakashi Gaiden).