Chrism - there is a way ....

You can get CP for example in USA to book your flights. Then tell them you will pay for and pick the ticket up in Canada. They will then quote you the Canadian fare.

But you would physically need to be there in Canada to pick up the ticket. Or else as was mentioned here - get Amex travel in Canada to issue the ticket for you and to courier it to you in the US. You must however, still start from Canada.