The Shipping Section of the Sell Your Item Form gives separate sections for Domestic/Canada shipping and International shipping.
Choose a service.
If you are using LetterMail within Canada, click on Flat Rate Shipping.
Weigh your parcel and insert the amount you need to cover postage and packaging.
Go to International Shipping
Go to Ship To
Choose Custom Destination
Choose USA
Enter Lettermail
Enter the cost of shipping (You can get postage rates at canadapost.ca or at your local PO in a brochure)
Choose Offer Additional Services
Choose Custom Destination
DO NOT CHOOSE N and S America - it will overide the previously chosen USA rate
Choose the countries you want to ship too.
Enter Lettermail.
Enter the cost of shipping.
And put the next dropdown as Will Ship Worldwide. (NOTE ; you can also set up a Block against countries you don't want to ship to.)
And down a bit more, enter the weight of your package, and the dimensios. Use metric. You may have to set this through the Options button (a blue question mark).
I'd tell you about Calculated Shipping, but I want to have my lunch now. Get LetterRate sorted out then ask again.
(NOTE: For your small inexpensive items, it would be worthwhile adding this amount to your asking price and then offering Free Shipping. There are several advantages to this. Customers love it, even though they understand the asking price includes the shipping cost. And eBay gives you 5 star s for shipping cost. And you pay no shipping FVF even on international sales, if you offer free domestic shipping.)