Combined from customizing shipping by destination:

Is there a way to customize shipping for additional items by destination? Adding a second item changes shipping costs dramatically for international locations. Right now, I have additional shipping charges for international buyers listed in Choices, on top of the additional item charge. But buyers don't always choose the right combination of shipping options, and if I have to send a new invoice, it's inconvenient and I incur another PayPal fee. It would be ideal to have the cart calculate shipping by location and weight automatically. Also, do Choices function differently now? It used to be that if the buyer chose the "additional item, international" choice, they would just get charged that cost once. Now they are charged that fee per item that they purchase.

and Canada Post