I will ship to Canada most of the time. It really depends on the item. For me it can be more work. It can also involve travel time to the USPS and a customs form to fill out.
Also, there are more variables to learn above just working on USA deliveries.
USPS International First Class Mail is a maximum of 4 lbs. Above that, you have to go to Priority International which is expensive. If the buyer wants it though I will ship it.
I use Pay Pal shipping which keeps me in my little world, never having to visit the USPS. If someone asks for Canada I will usually add the shipping options to the listing and let them decide.
I just shipped 5 lbs 3 oz of drum parts to Canada and it was $28.50 and I had to go to the USPS to do it.
David