I scoured the CRTC site with their search engine, and although I found dozens of differing references to advertising, I couldn't find anything specific to a "law" in Canada (that doesn't mean there isn't one; the website has thousands and thousands of rulings and regulatory statements).

What I did find was permissions being granted to a large number of specialty channels over the years, allowing them to increase their advertising from 8 to 10 to 12 minutes per hour. And these are the channels we pay extra for! Now, you know and I know and the whole population knows that we get six to eight minutes of advertising at the top of every hour... so I guess the limit is quite high. Way high. Too, too high. Holy skies, Batman. Way too high. ... Mike