The Grey Cup is a de facto national holiday, and I'm sure Parade Organizers knew for months the game was on November 19, and yes, the city should stop when the home team is in the big game: just ask anyone from Calgary, Edmonton, Regina or Winnipeg.
Last year the parade was the same day as the Western Final, but it was in the morning to avoid the conflict. This year, the parade is at 1:00 PM, and runs for a couple of hours. If one stays for the entire parade (which parents have to, since Santa shows up at the end), one is then forced to fight their way through the crowds/traffic having already missed the 3:00 PM kickoff. Most people living in the Lower Mainland would at least miss the first half, while a significant number would miss the entire game.
It hasn't escaped my attention that a major sponsor of the parade is Global TV, who have a vested interested in destablizing a CBC audience. It wouldn't surprise me that Global won't mention this (or the number of homes without power this weekend)when they pitch their Sunday NFL telecasts to local advertisers.