If your item is valued over $20 CDN (about $14 USD) you may have to pay duty.
If your item is assessed for duty, you will also be charged for sales taxes, even if no duty need be paid.
Plus the carrier will charge you for wrangling the parcel through the border. This costs between $5 and $25+ depending on the carrier and the value.
http://www.cbsa-asfc.gc.ca/import/postal-postale/menu-eng.html
