Bill Walsh started scripting plays for the 49ers back in the 80s. They say it was 15 plays he decided was best. They would practice those 15 plays and the team would know them backwards and forwards. It seems he decided those 15 plays was what was needed to figure out the defense and after that, you call plays based on what you learned in the first 15.
He would however come off script as situations dictate. So if you wind up 3rd and 1, then may come off script for a short yardage play, or if they get close to the endzone, they would come off script.
As for Canada, i'm not sure he scripts at all. Or maybe he scripts a bunch of plays and it takes them until almost halftime to get through them with all the 3 and outs.