Today we can confirm the deal is true, and now available to Lumia 950 XL buyers in Canada.
There you can purchase a Lumia 950 XL for CAD $849.00 and receive a Lumia 950 worth CAD $749 for free. Both handsets are unlocked and available in White and Black.
The deal is likely a consequence of slow sales of both handsets which has resulted in a build-up of inventory.
At present the deal does not appear to be available in UK and USA yet, and Microsoft may only be offering it in their slowest markets.
Update: This deal is now live in US too. Get the deal here.