Was your listing in CAD? Because I'm in Canada and I only pay with paypal and when I send money it get's sent in whatever currency the item was listed in. I don't get a choice, it's automatically done for me.
Paypal should convert the funds for you, however CAD is worth less that USD, so unless it's a higher dollar amount it's not going to be an equal amount. I would suggest contacting paypal, they would be able to answer your questions in a more informed manner since they can see your account, the transaction in question etc.