To the best of my knowledge, here is how it works:
USPS (US Postal Service) does not charge brokerage fees, but UPS/FedEx do. (So we always ship to Canada via USPS!)
CanadaPost charges a flat $5-per-package administrative fee when they deliver the package. They also charges sales tax at that point.
I think, though, that packages valued at less than $20 CAD are just delivered with no fees collected. So if your package was valued at exactly $20 USD ... that could be over or under $20 CAD, depending on whatever the current exchange rate is.
Some countries, such as the UK, do an exchange rate determination once a year. I don't know if Canada does that too.
Canadian quilters, here is a "definitive" link to follow:
http://www.cbsa-asfc.gc.ca/import/po...roits-eng.html ... it's a government site, so I would expect it to be up-to-date and correct. Here's another link too:
http://www.cbsa-asfc.gc.ca/import/po.../menu-eng.html
(We post these links on our own website, to help our Canadian customers.)