In previous years, the passes were valid from November - April, but Disney's starting to get chintzey on a lot of things and, as Grover says, this year they were only valid from January - April. If the economy stays in the tank they may expand the Canadian deal back to November and December in the same way that they've got AP room rates right through December 24 this year. Be aware, though, that if they return to the old time period for the deal, there has in the past been a blackout period around Christmas and New Years when the Canadian deal passes aren't valid. If you're going in early December that wouldn't be an issue, but if I recall correctly, in past years the blackout dates were something like December 22-January 2.
I guess all will become clear when they announce their plans later in the fall.
- Mike