If you have no tracking from Canada Post and did not purchase third-party insurance, you have no way of initiating a claim with anyone for a lost package. I'm sorry to tell you this.
Also, I believe most Canadian sellers only ship to China with tracking for the reason you are experiencing. If they ship there at all.
I can assume from what you've written that the buyer went directly to the Resolution Centre and that you now have a freeze on those funds in your paypal account? There's nothing you can do but refund the money to the buyer. As the sender, you need Proof of Delivery, not Proof of Shipment. Without it, you've no seller protection whatsoever.
It is a hard lesson learned. Unfortunately.
But perhaps another member can give you a different opinion that might offer more hope.