The reason you can't own a Canadian, gh, is that you are one. Therefore Canada is not a neighboring nation for you. Of course you could own an American. (And, from what I've heard about wages paid at T&FN, you apparently do.)
For Americans the issue is just slightly more complex. It is clearly absurd and even offensive, in this age of political correctness, to suggest that you can own a Mexican but not a Canadian. Canada and Mexico are equally neighboring nations. I have many devoutly religous acquaintances, who abide strictly by scripture, who own both. There is no scriptural violation there. However, they state that Mexicans tend to cost less than Canadians. Therefore it may be possible that in some cases an American couldn't own a Canadian because they just can't afford one. Whereas they can afford to own a Mexican. This is where the idea that "you can't own a Canadian" comes from. It's not a matter of scripture, but one of affordability.
I hope this clears up any confusion about the matter.