I don't know about the $15 limit, it sounds low considering the cost of shipping by Canada Post and couriers are even higher.
However, go to the customer's Paypal payment.
Click on Payment From John Q Doe.
This will take you to the Transaction Details.
Scroll to the bottom of the page and click on Print Shipping Label.
You have to choose the service next and enter some dimensions etc.
LetterPost is not available.
Your item is 'Other" not Documents /Sample/ Gift
The code (I forget the name) is available on the CBSA website. Just enter the name of the code. (Sorry not to be more helpful - the senior moment collided with the blonde moments)
You don't have to print a sample. You might as a learning experience.
Click to print.
If you have any problems come back here.
Take your time. You can't put it in the mail until Monday anyway.