You won't typically pay duty on these packages, but you will pay taxes (federal and provincial - rate can vary from about 5% to 13% depending on what province you're in), plus a brokerage fee from the organization collecting the taxes.
The brokerage fee will depend on the method of sending the package. Canada Post is generally best and most predictable, charging $8 (a package from the US would have to be sent USPS to get delivered by Canada Post). UPS and FedEx charge wildly variable brokerage fees - particularly UPS, where the fees can be tens to hundreds of dollars if the package is valuable. UPS' most expensive overnight shipping does not charge this fee, but of course the shipping fee is less reasonable. FedEx charges more predictable fees, but it will depend on the specific method you use.
Another option is to order from B&H Photo Video, which has made arrangements to pre-collect your Canadian taxes, so the package will arrive without any additional fees.
When the fees are payable, they are collected when the package is delivered. There is minimal bother other than being available to pay.
It is possible to clear your own package through Customs,if you use FedEx or UPS, and I know some people who have done this, but it will add some delay in getting your package, although it will save you the brokerage fee.
With Canada Post, packages valued at under $25 Cdn come in without any charges. Sometimes the package can be significantly more valuable and you will get it tax-free.
One final option: if you will have a rental car, you can have the packages delivered to a package service in a US border town, and go get the packages. Expect to pay federal/provincial tax still, but no brokerage fee (you're the broker). Package services generally have a per-package fee to accept your packages.
Finally, of course, if you buy from a Canadian seller, you won't pay any tax at all unless the seller is a retail establishment.