Provincial Sales Tax (PST) and our national Goods and Services Tax ( GST) are mandatory - and are enforced - on all internet purchases.
For most commercial purchases, this means they are always taxed, no matter where purchased. Goods bought in the USA will still be taxed by Canada Customs. If you used a courier like UPS or FedEx - the courier will charge you both the taxes and a
hefty handling fee ($30+) for collecting this piddling tax, too. If there are duties on the product (as happens with goods bought from the USA which were, in fact, manufactured elsewhere and thus not exempt under NAFTA) the duty on that product is collected as well by the courier.
If the article is mailed via the US Postal Service, then it is delivered here by Canada Post. Again, the post office collects the tax before you get the parcel. While small purchases and those marked gifts (if they appear to be fairly cheap) are frequently let through untaxed, for the most part on even small commercial purchases - the tax is actively collected by Canada Post . This is so whether you want to pay it or not. It is NOT an the "honour system".
So yes - sales taxes are always levied for all intents and purposes. PST varies province to province, but combined, they average about 15%, with PST and GST taken together across Canada (although Alberta does not have a PST. They have oil

) Free healthcare costs money
Because taxes are always payable, they are a neutral factor in any online shopping decision. The $5 handling fee charged by Canada Customs on a per order basis, however, is not a neutral tax and is intended to increase prices to make small internet purchases originating in the USA unattractive. The tax is clearly protectionist and is probably illegal under NAFTA, but has never been challenged with any vigor.
The reality is that shipping costs already have more than enough deterrent effect.