I can see that you are on the right track in the pictures. One antenna is pointed at the american stations and the other antenna is pointed at the Canada stations. The antenna that is pointed at the Canada stations needs to be at a 90 degree angle (side ways) to the American stations. And the antenna that is pointed at the American stations needs to be as close as the antenna can be to a 90 degree angle (side ways) to the Canada stations and not lose to much signal strength from the American stations. Flat panel UHF antennas have Minimum reception at the sides of the antenna. . Yes separate the antennas by at least 15 inches , this is the length of the metal receiving elements of the UHF antennas and the separation will reduce cross talk between the antennas. Put the American antenna on top and the Canada antenna on the bottom. I also suggest a Winegard CC-7870 antenna combiner and use a Winegard AP4700 UHF preamp on the power passing side of the combiner for the American stations. Here is a place in Canada to buy Winegard ,
http://www.techdepotcanada.com , T . Try the American antenna with and without the preamp.