I have purchased 3 lenses from Canadian sellers. I live in Indiana, USA. All three sellers sent me a tracking number, which was provided by Canada Post. Canada Post and USPS web-sites operate in the same way. You enter a number to track, the response is the latest scan of your item. When my items were handed over to the USPS, Canada Post informed me of that, and told me to track the same number at USPS.com. I did. It worked. I was able to track my items all the way from Canada to delivery.
I, being a cynic, believe you are being scammed. But, it is entirely possible that the seller lost his mailing receipt, and does not have the number. If that were the case, why would he give you a false number? OK, he made a typo when providing you the number, THEN he lost the receipt. It all sounds legitimate to me.
None of my items took a week in transit. Paypal has nothing to do with shipping. They just relay the number the seller enters. I am sure if you typed in ABC123BabyYouAndMe as a tracking number, PayPal would relay that to your buyer. Meaningless.
In your seller's defense, I shipped a lens, via USPS, from Indiana to the Seattle area. It took 16 days to get there, and it was not scanned after it left Chicago, until the delivery person scanned it as delivered. Weird stuff happens.