CAO 20.18 is a long read and requires some shuffling between sections.
I may well be wrong, but the way I read it, if in Class C or above A100 in Class G, both TSO 146 GPS and Mode S TXPR will be required to enable ADSB out capability in this airspace. If in Class G below A100 you could get away with TSO 129a and Mode S TXPR. When ADSB out below FL290 in all airspace becomes mandatory you will need to fit the TSO 146 GPS.
Mode S - Note The requirement is for aircraft to be fitted with a Mode S transponder with ADS-B OUT capability. That does not mean that ADS-B OUT transmission is also required under this paragraph. It means that, with the later connection of compatible GNSS position source equipment, ADS-B OUT can be transmitted as well as Mode S SSR responses.
I think this is the correct interpretation?
The cone heads I have been talking to say that a lot of operators and private owners have stuck their head in the sand for various reasons; cost and dates of compliance being a few. They say, come crunch day, a lot of aircraft will be non-compliant and there will not be enough avionics shops to go round.
.