They don't charge any duty or taxes if the value is below $20 Cdn. Most of my international purchases are below the threshold. And it seems to me that I've had things come in that were a bit over $20, and they still didn't bother to collect anything. If they do charge anything it's usually just taxes and not duty. There's a 5% federal Goods and Services Tax (GST), plus provincial sales tax (PST) that varies from province to province. Where I live, the PST is 6% for a total of 11%. In many cases the post office collects only the federal tax. The post office the best delivery service in this regard, because they only charge (last time I checked) a handling fee of $4.50 if they have to collect any taxes or duties, and no fee if they don't have to collect any taxes or duties. So, in most cases my package arrives at my door with nothing for me to pay.
Some of the shipping companies were charging outrageous "brokerage" fees that could end up doubling the cost of the item. "Pay us our brokerage fee, or we won't give you your package." UPS was one of the worst in this regard. I have no idea what UPS does these days, because I won't deal with them.