Depending on how the item is classified by the shipper, a small package can range from zero fees to just paying your province's tax. I've had new fuel injectors shipped to me as "warranty return" and paid nothing but the initial $7 USPS shipping charge. Canada Post isn't even that cheap for shipping within Canada. I've only ever heard of USPS or Canada Post charging brokerage for large items. Depending on where the item was manufactured there might be duty on it if the customs officer is having a bad day.
A few years ago, I bought a fuel rail and regulator for my car that was on sale in Oregon for $150usd. I told them to ship USPS, they confirmed, then shipped it UPS anyways. Cost me $60usd at the door, after paying $20usd to ship it. At the time, the exchange rate was complete balls, so in the end I was into it for almost $300cdn. Company that I bought it from wouldn't do a thing about it, not even store credit for the $60usd as a sorry.