Why is product placement rare in Canadian shows?

I watch a lot of shows from Canada, but not much product placement is shown compared to the United States, United Kingdom and Australia. This excludes reality shows, documentaries and shows co-produced in another country or filmed in Canada but produced in somewhere else like America. Shows where I have seen some product placement include Naturally Sadie (Scrabble, Jeep and Honda), Black Hole High (Twister, Sanyo and Audi), The Adventures of Shirley Holmes (Hershey's Cookies & Cream and Kodak), Monster Warriors (Volkswagen) and Dinosapien (Chevrolet).

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