Does it have to be canon? 'Cause 'till S6 E10 Caged Heat aired, I was abso-fuckin'-lutely sure Dean and Castiel were doing it. With all that sexual tension and references between them it just seemed natural as rain that those two had the hots for each other. But hey, they still might have a romance going on, without any kind of sexual acts included, right? Or maybe I'm just a too big of a slash fan to let go of the image of those two together.
Oh well. Let the subtext speak for itself!