PappyJ..
There is no CARs reference. Here is the AIC on GPS use:
http://www.navcanada.ca/EN/products-...008_16.pdf#top
Look at paragraph 6.0(b).
Second reference is paragraph 3.15.5.2.2 in the TC AIM which you can search for on the internet:
"Unless required by the aircraft flight manual (AFM) or AFM Supplement, it is not necessary to monitor the underlying navigation aid, and it is even permissible to fly a GPS overlay approach when the underlying navigation aid is temporarily out of service."
Elephant..
Overlay approaches are allowed provided the raw data is displayed. What is not allowed is turning a normal approach into a GPS approach because the relevant aids are not available (or you do not wish to display them), for that you need a specifically published GPS approach.
You can't just turn an approach into a GPS approach. It either isn't a GPS approach or it is - you, as the pilot, cannot make a GPS approach.
The GPS approaches include RNAV approaches, overlay approaches, and RNP approaches. I've provided two references for GPS overlay approaches in Canada not requiring the underlying NAVAID to be serviceable or monitored. Do you have a reference for what you're saying?