You'll have to pay GST, as far as I know there's no duty on bicycles. I've only ever got parts imported and they are duty free. You may have to pay PST as well, depending on which province you live in. Here in BC bicycles and parts are exempt from PST, last time I got something sent by FedEx they tried to charge it, so watch for that.
If you're using FedEx or UPS they'll charge you a brokerage fee, about $40 or so, for doing the paperwork. A lot for almost no work but you don't really have a choice.
If you're getting stuff sent more often and live near the border it works out cheaper to use a shipping company on the US side. I use one just over the border in Washington. I get much cheaper, or even free, shipping as it's a US address. For small stuff Canada Customs quite often just lets it go. For the more expensive stuff I just have to pay GST. The shipping company charges $5 - 10 US depending on package size, I drive down and pick it up, and save $10 by filling up with gas while I'm there .