According to a couple of threads (here and here) on Atari's community forums, most if not all copies of The Witcher shipped to Canada are missing their CD key. The good news for those of you affected is that the CD key isn't required to launch the game - it's only required to register on CD Projekt's official forums. Apparently you can email Atari to get a replacement key, but none of the members reporting the problem seem to have had any luck with that method just yet.
On the bright side, this is just another good reason to import the European version.