Are you using the Sell Your Item form? The longer , 2-page one?
Below Domestic Shipping is International Shipping.
Choose Calculated Shipping*
Choose Custom Destination.
I assume you are also shipping to the USA?
Choose USA.
Enter service.
Choose Add Additional Service
Do NOT choose USA or N& S America
Choose from the countries given.
Enter service.
If you want to ship worldwide, leave the next option as Contact Seller for Costs.
Enter dimensions and weight.
Use metric measurements.
If your S&H is still disappearing, go to canadapost.ca and check that your METRIC dimensions will actually match the services you have chosen.
Canada Post went metric in 1974, forty years ago. Any other measurements will be approximations and often inaccurate.
* Or Fixed Price, but Calculated is more precise.