As a frequent purchaser of US goods, I much prefer USPS over the other couriers. So much so, that it influences my purchasing decisions. UPS within Canada is just fine, however as soon as it crosses the border, the fees become just silly.
As far as I'm aware, USPS charges no brokerage fees for items valued under $500.
Everyone here expects to pay tax (GST/PST/HST) and duty seems to be hit or miss. I've often crossed the border with items which have no clear "made in" statements, or "assembled in", in which case customs usually gives you the benefit of the doubt.
Another bit of information which may be useful for larger purchases (for consumers): If you live in a city close to the border (which is a large percentage of Canada), a quick trip across the border to a holding warehouse can be easy, faster, and cheaper than letting a courier do it for you. For example, I might have something shipped to Blaine or Point Roberts in Washington State (where there are many companies who will receive and hold a package for you for a nominal fee (~$5). Obviously it doesn't make a lot of sense for small items, but for larger items, if the shipping stays within the US, it is often significantly cheaper.