Summit has free shipping to Canada

When I ordered, at checkout summit charged $55 extra for duties/taxes.
If shipped by FedEx, I believe you will get hit with a customs processing fee

No, because everytime I have ordered from summit and shipped to my home address in canada Summit has collected the tax at the time of purchase.
The odd time the part comes from Ohio the package does not seem to get hung up at customs. As long as the tax is collected at time of purchase then there will be no brokerage fees.

Majority of the time the parts seem to ship from Mississauga

That's why I posted the special Rob, our selection is poor and pricey. I imagine quite a few of the Canuck retailers are reselling Summit stuff anyway.
We have a few Karbelt speed n custom, Performance improvements but none with price and selection like you Yanks got lol.
They might be fishin to see if they can swing doin it on a permanent basis. You never know. Strike while the iron's hot.