Using the small supplier exemption seems really doubtful to me. That pushes the tax collection liability on the driver (who can't collect taxes, since payment is through Uber app) and the limit for that is 30k$ so a lot of drivers should probably have charged taxes since they may have earned more.

In addition, my understanding (not a tax/law person) is that the 30k$ would be for the whole fare, not the driver's cut.

GST rate is 5%... But provincial sales tax could apply, at least in provinces where there is HST (Harmonized Sales Tax, administered by fed gov, divided with province.) HST varies from 13% to 15%. I wonder if we'll see provinces going after the drivers for back taxes. Revenue Quebec is notoriously aggressive in going after people for sales tax.