If Carney really wanted to turn the screws to the Yanks, just put in export tariffs tomorrow. On just oil.
The USA needs every drop of oil right now with them drawing from the SPR, if Canadian oil had a export tariff (paid by the importer, so one case where foriegners actually pay the tariff) the yanks have two choices.
1. Import less Canadian oil, drawing down the SPR even faster, pretty much Canada teaming up with the Iranians to pressure the USA
2. Pay the costs, driving up prices in the USA even more.
Granted, the wrath would be epic. So would the fury.