You cannot prove that. There is actually a lot of evidence pointing to the movies being canon. If anything, Pokemon 2000 isn't canon because Ash never recognized an Articuno after that.
Right now I'm expecting this to be the second Unova movie. We'll probably get another trilogy again. They're being released so close together though, so maybe they'll both be short. <_>
First off, Pokemon 2000 is canon. While in the Whirl Islands Ash mentions he met a Lugia in the Orange Islands a while back. Yes there is the DUB error with him implying he has never seen an Articuno.
Second, I haven't seen a few of them in a LONG time so I don't remember every single detail in the movies For example:
-I didn't know about Dawn and the Lunar Wing.
-I thought there was one more instance where Ash met a Latios. There isn't so my mistake.
-I remember Drew was from LaRousse city, but I don't remember if it was ever mentioned in the tv show.
-I'd have to watch the Riolu episode to hear exactly what was said about Ash's aura abilities in the tv series.
-As for Mewtwo vs Gary, I do remember that it just slipped my mind.
So they ARE canon to the tv series - my mistake.