Use Calculated Shipping.
You will have to choose Custom Destinations outside of Canada, but if you do one section for USA and one for Overseas (start with UK and Europe, but Australia is pretty safe too.).
You will be asked to choose a shipping service. Only use AIR MAIL for overseas. Do not choose Small Packet Surface USA, as this no longer exists.
You cannot choose Letter because that is not an online service. For USA and overseas you can choose Light Packet.
