The trick is to avoid US sellers that insist on using Fedex and UPS, and never buy from any Ebay seller using that new Ebay global shipping rip-off program(someone is making a sh**load of cash from that one!) I find that with shipments via USPS with a hand-off to Canada Post I never have to pay duty or taxes on anything under $100, and sometimes I don't even get charged on packages worth more than that.
On a side note, when I see something I want on ebay but the seller is using EGSP, I send them a note asking them if they will send via USPS and explain why. Most of them had no idea that it was a total rip-off on the buyer and are more than willing to accommodate my request. I've known a few to dump EGSP entirely because of the information I provided to them. I'm on a mission, one seller at a time!
As to Canadian suppliers, I deal with the Porsche dealer here in Winnipeg and they've been really good. Their prices are about what you would expect, and they give a 15% discount to PCA members. I can't type their name because it just comes up as ******** like it's a bad word or something. I don't know what's with that, but it's kinda strange. Think German for "Car House".