Tell the buyer that Paypal will only print the shipping label with an address that the buyer puts in and ask him to change or add the "gift" address.
If it is a gift, the usual reason for requesting a different destination, he can add about a dozen different addresses.
If he gets stroppy, you can be firm about shipping to the Paypal address. But I would plan in that case to pay the extra for Expedited shipping. Purchased through PP it will be 20-25% less than at the PO counter. Expedited includes both $100 insurance against loss or damage in shipping and Delivery Confirmation which is useful if a PP dispute on non-delivery comes up.
PYA.
But it probably is a gift. And Canada Post is very reliable.