Before trying to answer your question, why do you want this list? If you want to only visit restaurants that take Amex, I would advise against it. You'll be missing out on a lot of gems.

To vaguely answer your question, I'm based in YYZ and occasionally travel to YVR for work. Almost any restaurant in the downtown core for both cities that has over 15-20 tables takes Amex. It's almost guaranteed that any chain restaurant will take Amex. When you go outside the downtown core is when you'll start getting more hit and miss, especially when it comes to ethnic cuisines.

When I dine downtown, I use Amex over 90% of the time.

Most restaurants will have stickers on the front door telling you what forms of payments are accepted.