This was trialled at JFK some time ago and was a failure with a very low rate of uptake. Lounge capacity at outstations is also an issue - IIRC YYZ is pretty small - and if you start allowing paid access your premium pax may not have space. Building a bigger lounge isn't an option as a few people paying an extra USD30 or so won't offset the huge cost of taking more space in an airport.
Have you considered Priority Pass or similar?