In my experience even on registered mail if it's a big order you might get hit by a custom fee , but if I remember correctly it's way less expensive thant a DHL one. I believe Canada Post it's pretty much random but DHL every order got hit by customs :xI feel your pain. I once got 55$ CAD (42 USD) custom charge from DHL on a 176$ USD order.
I use normal postal service now and hope it takes less than a month... I'm currently still waiting for an order places January 14th...