okay but just…imagine, for a second, that it’s the series finale of Supernatural. Everything is about to go to hell. The big final battle. More than likely there won’t be any survivors. And just before they head into the fray, Team Free Will pauses, one last moment of quiet. No words, just silence, and then the camera pans down and we see Dean and Cas reach out and take each others’ hands.
And that’s how it becomes canon.