As we know, Canadians love to be the fodder for monopolies. Most of the stuff we buy here comes from shelves that have been bought out. As such, we pay a high price. Now, it comes to pass that certain things cannot be bought here at a high price, or we just feel cheap. Then we get stuff from the States.
I really feel cheap about small electronic things, especially when I'm looking at a Canadian multiple of several times. Try buying a special cable adapter, or a phone case. Most of time, I have found amazon.ca to be quite good in that they ship from a lot of small US stores and they know how to send things to Canada by cheap mail. We get phone cases that way.
But sometimes you want something weird. For example, shade cloth for the pergola. Can't find a good selection here at all. Or, a motion sensor switch that works for LED lamps. Then you go to speciality US shops who have never heard of Canada, or if they ship, it's a horrendous cost. In those situations I use my US shipping account over at myus.com.
Not easy to pay for these things at the hick stores. You need your US shipping address on your credit card, and even then it never works. I've been using Paypal. If you use it one way, such as 'Pay with Paypal' on the vendor site, it only lets you put in a Canadian address. But I have found that certain sites let you fill in the US address first, and then you can click Paypal. That way I got in a US address, but it wasn't easy. Now I have a permanent second address in Paypal and I can go anywhere.
Update: I am removing all the fine suggestions of other shipping services, since I can't tell them from spam.