Well here's something else to chew on. A more accurate number for Canadians who served in the US military in Vietnam is found on this page

According to the website, approximately 5,000 Canadians joined in the fighting in Vietnam, based primarily upon mortality rate. Exact figures were not kept by either the Canadian government or the American military.

Other significances aside, those Americans who came north to Canada and those Canadians who ventured south to volunteer for the US military, in numbers, were a very small portion of either countries over all population.