The S20 and S20+ can only charge up to 25W. They kept the 45W charging for the Ultra. Likely as a money grab to try to get more people to buy the most expensive version. Also, the Note 10 can only charge up to 25W. They saved the 45W charging for the Note 10+. I’ll grab some links so you can verify.
Fastest / best car charger for Galaxy S20
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From what I understand based on the research I’ve done myself for similar reasons PD and QC 3.0 are going to be about the same if they have the same wattage output. Overall PD is better because QC 3.0 has a max output of 18W, while PD has a max of 100W. The issue therefore is finding a PD device with the output that you want. If you want max charging speed you’ll want to get the Samsung charger that can charge up to 45W. I haven’t been able to find a PD car charger with 25W output. Though, it seems you’re in Canada and like you said it seems unavailable for you to purchase there for some reason.
Thanks for the links and correcting me 
The PowerDrive III Duo is a good charger.
I elected to go with the PowerDrive+ III Duo to charge my smartphone (18W) and iPad (30W): https://www.amazon.com/Charger-Anker-Adapter-PowerDrive-Delivery/dp/B07YY7KQZP