The Global Shipping Program is run by PitneyBowes who act as trans-shippers for US eBay sellers. Your seller sends your parcel to Kentucky from where it is sent to Canada.
The breakdown of the $81 is hard to tell without seeing the price of the item you bought, but basically it is made up of:
A few dollars to the seller to cover the cost of shipping to the PB centre.
A service fee to PB for processing the Canadian sales tax and duty if any.
A shipping fee to PB for trucking the parcel to Canada and from there to your house.
Canadian duty if any.
Provincial sales tax.
GST.
Your seller is protected against bogus non-delivery claims once the item is Confirmed as Delivered to the Kentucky warehouse. This is good news for US sellers, especially those who are nervous of shipping to strange countries like Canada, Hawaii, or Panama.