"That rule allows Canadian networks to ask TV providers such as cable and satellite companies to swap out the ads running on U.S. channels that appear on the dial, and sub in Canadian ads, when the same TV show is running on U.S. and Canadian channels at the same time."

Not exactly an accurate description of the process.  What they'd do is substitute the Canadian feed completely on top of the American one, and by using automated timers.  This was super-frustrating back in the days of NFL football on Global.  At 7pm, the cable company would stomp over the end of the game with CBS's 60 Minutes, often causing us to miss exciting end of game plays.  We'd have to just sit there waiting for cable idiots to switch the feed back.  This often took 5 or 10 minutes or more.  Super frustrating.