COPPA is a US law not a Canadian law but with having the server hosted in the US you'd likely have your site classified as a US based website.
You're site won't be shut down if you don't follow the rules. You'll get a threatening letter from the BBB. At least that's who it used to be, it's possible the oversite is being managed by someone else these days. They'll tell you you're not following the rules and will give you some details as to what you need to change...of course not telling you how to change them or anything.
You're right that the act is from 2000 and would seem ancient in computer terms, but it still holds true.
As for 100% Canadian based websites it's good practice to follow the COPPA rules. In Canada we have guidelines (http://www.the-cma.org/?WCE=C=47%7CK=225849#11
) that we're supposed to follow voluntarily. If you follow the COPPA rules you'll be covered and won't have to worry about any ramifications form either side of the border.
On a separate but related point, there's also an ethical issue here. The spirit of the law is to protect the personal information of kids who may not know it's not safe to give away their real name and phone numbers. The law tries
to ensure a kids parent is informed of their child's activities online (to a degree)...setting aside the fact that kids will lie about their age to get registered.