If you bought a Windows 7 PC (laptop or desktop) since June 2, 2012 you are eligible to upgrade it to Windows 8 Pro for $15 (which is a pretty great price!). This time around there also won't be any complaining about the US vs. Canadian price since the price is the exact same for US and Canada. Canadians will also be paying in Canadian funds. It's nice to see a level playing field for US & Canadian orders.
Up until now you had to sign up at Microsoft to be notified when you take advantage of this offer. Well today is the day. You can now to go http://www.windowsupgradeoffer.com and register for your upgrade. You'll need the following information:

Contact Details
Email address
Phone Number
PC make / model
Purchase date
Retailer / PC Manufacturer
You will then go through the validation and confirmation process.

Don't get too excited yet. You won't be getting Windows 8 Pro right away. According to the Microsoft website:
Windows 8 can be ordered beginning on October 26, 2012. When Windows 8 is ready for ordering, you will receive an email with your promotion code that you must redeem to receive the promotional pricing during the upgrade ordering process. This email will also include ordering and download instructions and a link to the ordering website.

This upgrade is a download only (approx 2GB) - you will not be sent a CD with Windows 8 Pro.