It's become a bit more complicated thanks to the latest North American free trade agreement. I'm not even sure that I have it right.
My understanding is that items shipped from the United States or Mexico have a duty-free limit of C$150 and a tax-free limit of C$20 if sent by mail, C$40 if sent by courier. I don't believe the items have to be manufactured in those countries to qualify for the duty-free limit; they just have to originate from those countries.
Items shipped from anywhere else have a tax and duty-free limit of C$20 if sent by mail, C$40 if sent by courier.
EDIT: This calculator from our friends at the CBSA may be of some help. I see that one of the questions it asks is if the item was manufactured in a CUSMA country, so country of manufacturer might be what determines its duty-free status, not the country of origin, but the calculator seems to be designed for travellers, so that might make a difference:
https://www.cbsa-asfc.gc.ca/travel-voyage/dte-acl/est-cal-eng.html
EDIT 2: This CBSA page seems to spell it out pretty well:
https://www.cbsa-asfc.gc.ca/publications/cn-ad/cn20-18-eng.html