US-Canada also has that element of small-versus-large - the US looms (I imagine) much larger in the Canadian consciousness than Canada does in the American one,

US-Canada also has that element of small-versus-large - the US looms (I imagine) much larger in the Canadian consciousness than Canada does in the American one, just because the US isn't so defined by that one neighbor. Maybe more like Portugal-Spain? Hard to find examples like that where there haven't been any wars in a couple hundred years, and there's also that linguistic/cultural similarity.