“One of the many routes for Canadian arms is through the United States loophole: Canadian-made deadly munitions and components are exported to the US, which are then transferred to Israel as military aid. By shipping arms to the US to be assembled into fighter jets, attack helicopters, and other deadly weapons systems that are actively massacring Palestinians in Gaza, Canada evades arms trade regulations and circumvents its responsibilities as a state party to the Arms Trade Treaty.”
You absolutely can tariff exports. Usually a government would only do that in order to disincentivize those products leaving the country, so it would be unlikely to ever happen because the Canadian government ostensibly supports war and genocide, but export tariffs exist.