I agree with the open skies thing...this is not allowed. UA can definitely not sell a seat ex-US to another US destination via Canada. AC can't sell an ex-CA ticket to another CA destination via the US. While I suppose a re-route isn't technically selling a ticket this way, I would imagine that this is still not allowed.I have even tried booking a ticket with AC that started and ended in Canada with a domestic US segment in between, and I still couldn't do this. I think I also tried this on UA too, but leaving and arriving in the US with a domestic Canada segment inbetween, and this too isn't allowed.