a retaliatory tariff on american prison labour by all affected parties, or even an outright ban on goods and services made in american prisons, would be a proportionate response that would also send a clear political message to the americans. 

i am generally opposed to placing tariffs on goods entering canada from the united states. canadians don't benefit by paying more for orange juice, or not being able to buy vodka. that doesn't help us. it's just a punitive tax on ourselves.

but we should not be supporting the continuing reality of forced labour in the united states' penal system. canadians should not be buying goods made in american prisons. at all. period.

further, i would not support lifting that ban or set of tariffs as a part of negotiations. i would keep that restriction, until they change their laws.