"Helped along by this proximity, Windsor – and Southern Ontario more generally – became the Canadian extension of Detroit with the help of two policies. First, there was a 35 percent National Policy tariff on cars entering Canada. This protectionist tax encouraged Canadian production by making Canadian goods less expensive than their foreign (mostly American-sourced) competitors. Second, since Canada was part of the British Empire, Canadian-made goods could be shipped to many countries in the Empire (later, the British Commonwealth) at a lower tariff rate than other countries, namely the United States." (quoted from The Canadian Encyclopedia, Automotive Industry accessed 8 July 2017)
