First go to your Paypal account and see if the money has in fact been taken from your Paypal balance. If you are smart enough to use a credit card with your Paypal account, that will show too.
If you attached your PP to a bank account, it will take upwards of 10 days for the e-cheque to clear.
Is the seller saying he has not received your payment?
This could be true. If you paid from a bank account, as above, it will take 10 days before he can print your PP shipping label.
If you paid from a card or a PP balance, and he is a new seller or selling in a high value/high fraud category, like jewelry, PP may be holding your payment for up to 21days against his good performance. However, he can print the shipping label, and is required to ship to you within seven days. (It can take a further 20 or even 30 days to arrive).
Is the seller demanding more money ?
A polite email telling him that you purchased on the basis of the advertised price and shipping and will not pay a penny more is all you need.
Is the seller using the Global Shipping Program?
You will have to pay the Canadian duty and sales tax before the seller will ship.
Post the listing number and give us some more to work with, please.