Go to Seller Admin > Cart Shipping Settings and set up the following:
Shipping Origin: select United States and enter your zipcode;
Shipping Destinations: if you will only ship to certain countries, select them in the list, or otherwise select nothing for Worldwide shipping;
Leave all other settings blank or 0.00;
Click Next to save settings and proceed to the Shipping Rules screen.
In the Existing Shipping Rules menu, select and Delete any Rules you may have saved there.
Set up a Shipping Rule for Domestic shipping:
Shipping Rate Calculator: Flat
Shipping Amount: 0.00
Country: United States
Click Submit to save the Rule.
Set up your first Rule for Canada:
Shipping Rate Calculator: Flat
Shipping Amount: 9.95
Country: Canada
Max. Item Total: 50.00
Click Submit to save the Rule.
Set up your next Rule for Canada:
Shipping Rate Calculator: Flat
Shipping Amount: 14.95
Country: Canada
Min. Item Total: 50.01
Max. Item Total: 100.00
Click Submit to save the Rule.
Continue setting up Rules for Canada; your highest-tier rate can leave Max. Item Total at 0, meaning "no maximum".
Set up your first rule for "rest of the world":
Shipping Rate Calculator: Flat
Shipping Amount: [enter your lowest Int'l rate]
Country: All Countries (covers the rest of your Shipping Destination countries which don't have Rules of their own);
Max. Item Total: 50.00
Click Submit to save the Rule.
Continue setting up additional Rules for all your international rate tiers, similar to what you did for Canada.
Click Back to Admin, and you're done!
