Canada Post charges a $9.95 handling fee only for items imported into Canada that the CBSA flags for duties and/or taxes... USPS/CBSA do not receive any of the money charged for this handling fee. Merchandise (something you've purchased) imported into Canada, valued at <= $20, is exempt from duties/taxes. Gifts (something given to you by friends or family) imported into Canada, valued at <= $60, are exempt from duties/taxes.
In my experience, the CBSA rarely enforces these amounts, except when country leaders get into pissing matches. I've imported lots of items (excluding liquor/tobacco products) into Canada from various countries and rarely do I pay for duties/taxes when these items go through the regular postal system and are valued at <= $150... YMMV. As for private couriers... all bets are off.
Edit: The last time I paid taxes was for 550 CPS chips from Apache... valued at approx $220 USD and I think I paid approx $35 CAD total (taxes + handling fee).