As far as the law is concerned, I believe you will only have to pay GST (provincial taxes don't have jurisdiction), and this is the legal minimum you can get away with (and with our dollar how it is right now, it's well worth it most of the time). Unfortunately both UPS and FedEx will stiff you for huge fees for brokering your package. A UPS package with a customs value of ~$100 will likely cost you an additional $30-40 in brokerage and miscellaneous fees. Ridiculous to say the least. I think FedEx is a bit more reasonable, but be careful with these courier companies. I've heard reports of people saying that you can request to self-broker the package on the shipping end, and they can't ding you the fees, but I've never tried it. If you use USPS/CanadaPost it's pretty much a coin toss. Sometimes they don't even charge the GST, and sometimes they'll charge the GST (or whatever duty is required) plus a processing fee (though a reasonable one, like $5). CanadaPost usually sends a bill in the mail after the fact, I've never received a package where they've asked for COD duties. UPS has always required duties/fees COD.
The bottom line is to avoid courier companies, and if you can stomach the wait, have the shipper use USPS. GEM is pretty fast, and usually much cheaper than UPS not even counting the ridiculous brokeage. Unless you can cross the border easily to pick up the package at a receiver (I know of a couple in Point Roberts and Bellingham here near the BC border, I'm sure similar services exist in border towns near Ontario) for a small fee and cross the border with it yourself. I've done this a couple times here and it's usually much cheaper both for shipping and brokerage (the service charges like $2 a package and it usually saves ~$20 on shipping), but the people at customs have hassled me, and it may be quite a drive for you, so you decide if it's worth it or not.
