Technically you're right, but two points here. Firstly, in the mind of a Canadian, the US is about halfway between foreign and domestic. Most of us live an easy drive from the border, and have friends and relatives in the US. In our minds, it's not as foreign as Germany or France. It's more like "Greater Canada", to coin a term. So if they give you a hard time going in, it can hurt much more than if the same thing happened in, for instance, Mexico. Secondly, I've travelled all over the world, and have never been given a hard time at any border, except in the United States. Most of the people I know, have had the same experience. There is something about the way American border guards react to some people, which can be highly problematic.