I think you are confusing taxes with duties and tariffs. They all pick our pocket just the same but they are very different things.
Duties and tariffs are designed to protect local industries from foreign competition. If you have a steel industry that produces steel at $40/ton and some other country has a surplus and decides to dump it into your country at $20 a ton you have a problem. The consumer has cheap steel for a while but all his domestic steel plants go bankrupt. All the jobs are lost and then the foreign outfit can charge whatever he wants.
GST and PST are forms of sales and service taxes. Nothing to do with NAFTA. The trade agreement was to reduce and/or eliminate duties and tariffs. Ottawa and the provinces still nail us GST/PST when stuff crosses the border. So do the Americans when a Yankee Ebayer receives the Traynor you shipped them. Their governments both state and Federal are just as greedy as ours.
What's worse, we cut out the duties and tariffs but kept all the damn paperwork!
Canada loves to sign free trade agreements but we seem to be kinda simple about it. We force big extra costs on our steel companies to reduce pollution but we allow China, who seems to spend ZERO on pollution controls to ship their steel into our market! This is fair market competition? That's why Kyoto seems so ridiculous to me. It exempts China and India, two countries that have nuclear bombs and space programs from reducing emissions, when they are now or in the case of China rapidly becoming the biggest polluters on the planet. Without any cost of reducing pollution China has a HUGE trade advantage! We have a Carl Sagan type of trade deficit with China - you know, billions and billions! They sell billions of dollars of stuff through all the Wal Marts to us and we sell a couple of Nortel phones to them.
We do the same thing with agricultural products. Strawberry farmers in the Niagara area try to compete with strawberries air-freighted in from eastern Europe. Their countries subsidize the hell out of the cost.
Grape farmers for years used Alar, a chemical product that prevented various forms of grape blight. We banned it. Unfortunately there just doesn't seem to be anything else that works even close as well. Yet Americans in upper New York still use it and thus can charge cheaper for their grapes when shipped into Canada. If the stuff is so dangerous for us to eat on our grapes then why is it ok for us to eat it on foreign grapes?
I'm straying a bit from your original point, I know. I just wanted to show the differences and how in Canada they don't appear to make sense anyway.
Or perhaps they do? It depends on your goal. Are you trying to protect Canadian industries? Or promote increased trade and jobs for everyone?
Or just bleed us close but not past the point where we die?