NAFTA has nothing to do with "brokerage" or "tax". NAFTA is about duty. Without NAFTA there would also probably be duty fees on top of the tax and brokerage.
Brokerage fees are where the couriers really screw with you. Some don't really publish tables of fees and make things up when your item arrives. Others have tables of brokerage fees based on package value and which tier (speed) of shipping the package is.
The postal service BY FAR has the best brokerage practices. Brokerage fees are $5 normally and $8 for EMS packages. These fees are only charged if taxes are charged. Taxes MAY be charged on any package declared over $19.99 ($49.99 if marked "gift").
Of course I have seen agents open packages declared at $5 with a $40 invoice/packing slip inside and get assessed the full $40. Same goes for items they didn't believe were gifts. I've had EMS-class packages come straight to the door but be followed by an invoice for taxes/brokerage in the mail. I also had UPS charge me $70 in brokerage and fees to process a $35 used car audio item. Then they had the nerve to take me to collections claiming I didn't pay it when you MUST pay it to receive your package. I even showed them a canceled cheque and they persisted. Can you say "boycott" with me?
UPS and Fedex do have products which "include" brokerage in the shipping cost. These are usually their premium super-duper express services. That still doesn't cover the taxes you owe, however.
Of course the customs agents can "selectively enforce" taxation. Things valued over $19.99 might come through with no fees, or maybe they won't. I've been asked to pay tax on a $22 item, and I've also had $35 items show up with no fees. You simply never know. Your best option is always to ship USPS from US to Canada. So far it looks like my Filco from PCHome via EMS hasn't been assessed any fees. They didn't have to let it go, we may simply be lucky. I won't consider it closed until at least a month has passed and then I'll celebrate
The catch is that I cannot assume that every PCHome order will come sailing through with no fees, and the fees can make the difference between a PCHome price/hassle being competitive with something local or not.
As far as I know, Americans don't pay any tax/brokerage on typical items which they receive from outside of country. As far as I know, they also don't pay any taxes when ordering items out of state. Here if I order from NCIX in Vancouver I still pay my Ontario HST (13%). Another way in which the Canadians get screwed financially, presumably to fund our socialized health care.