You're right in that the legislation differs provincially. I will have to double-check, but I believe right now five provinces have mandatory referral written into their current legislation. It's also important to note that even the mandatory referral legislation differs provincially. For example, in B.C. there is a requirement to report all deaths of those younger than 75.
The way the legislation is currently written is quite different, and a few provinces still do not have mandatory referral legislation. A couple are in the process of getting it, that don't yet have it in place. It would be very helpful to ensure that was in place in every jurisdiction.