The seller is responsible for getting the purchase to the buyer in a secure and timely manner.
The buyer's first step, if he feels the shipment is late is to contact the seller, who should give the buyer the date of shipment and the service used. At this time the tracking number should be given to the buyer.
If the buyer is still unhappy, or if he skips the first step, he can open a Paypal dispute within 45 days of purchase. When was the item purchased? (not sent, purchased).
The seller can give PP the tracking number, but the question then becomes, where is the parcel? Theoretically it is in OK, but in fact that's just the last place anyone recorded it. It could have been delivered without the postie recording the delivery.
Ask him to go to his local post office and ask about the parcel, with the number in hand. It could have been returned there and the pickup notice lost or blown away. Stuff happens.
He should also ask the family and neighbours. If you use any unusual packaging (purple wrapping paper, Fragile stickers, address written in Sanskrit) mention that as a memory jog,
Tell your buyer that you are starting a trace through Canada Post and ask him to cooperate with the USPS postal inspectors. If he is messing around, that should put the fear of Ghu into him. If he is honest (and he probably is) that will reassure him. Start the trace at a Post Office not a postal outlet. Have your tracking number handy.
You could also do this by phone, but I would avoid the Canada Post email system, which is no better than any other online customer service centre. The phone ladies are very helpful in my experience.
Keep your buyer informed.
If he opens a PP dispute, don't panic. He needs this to keep his options open and he only has 45 days for it. Be sympathetic.
If CP/USPS finds and delivers the parcel, all is well.
He has 60 days to leave feedback and Detailed Seller Ratings. And he can leave a Response to feedback indefinitely.
Be as helpful as possible. Most people are honest.