If they pledge to support you while you're here, you need less. (Especially if you are staying with them for the entirety of the trip.) But it's still good to show you have the money.
Unfortunately there is no official amount you need to show. You have to prove you can afford hotels, meals out, activities, etc for the duration of your stay. I saw anywhere from CAD$1200 to CAD$7000 online, but that depends upon the number of people visiting among other things.