If you check the DTV beam maps vast portions of Canada are excluded. But the reality is that the beams aren't precise so the signal is available north of the border. And in the western portion of Canada DTV includes Alaska and SE Alaska. As a result a significant portion of BC and Yukon are covered.
The following information is incorrect. We had DTV service all along the Alaskan Highway with our RF Mogul dish which is a basic Slimline 3 and certainly not 7'. But the birds are very low and you do need line of sight. It would not surprise me if domes with there much smaller antennas would not work in Alaska.
Now if he says it won't work in Alaska I will agree with him. If you want to watch Directv in Alaska you will need at least a 7 foot dish and a clear view of the horizon at 10 degrees elevation.