Yeah, but Eddie and Adam cannot decide what canon is, that is the whole point. Their opinion doesn't matter. Their head canon about scenes while of interest, is not canon. There are many people whose thoughts on Ouat are of interest, that doesn't make them canon. Deleted scenes are not canon whether Eddie and Adam think they are or not. Canon exists outside of their thoughts, that is the very definition of canon. Commentary is not part of canon, it is head canon, it is commentary.
I think we are working under differing definitions of the word ‘canon’. What I mean by it is “the material accepted as officially part of the story in an individual universe of that story” (def courtesy of wikipedia). They’re the showrunners so they kind of do decide what happened and what didn’t happen. It’s a little different than some random commentator’s head-canon. If they’re making writing decisions based on things in deleted scenes and writing as if they happened, by that definition, yeah, it’s canon.
Like, there’s this scene in S4 where Rumple takes this magic dust from Elsa’s bottle and uses it to trap the Snow Queen. And it’s like, “Where the hell did he get that?” but, in a deleted scene they aired on GMA, you see him collecting it. You gotta assume that scene happened, even if we didn’t see it. Again, dumb but the reality of this show.