I really don't see the issue of people who have seen the episode early posting in the thread. The Canadian broadcast is just as "official" as the US one. Personally I find this whole thing rather silly. I'm tempted to just put every comment in spoilers, just to be petty, because the show hasn't started airing for the US military until the 7th of January. Obviously they're not to this episode yet, and I know we get some military folks on the boards. This is an international board, after all, and the owner is from the UK... and it just started airing there on the 19th of February... so shouldn't we not be posting until they see it there?
My rampant puerility aside, I see three somewhat obvious compromises here.
1) Where ever the show is shown first starts the thread. After all, there's no real reason for the discussion thread to be up before the day it airs. Once started, the episode thread is considered good for spoilers.
2) Put the Canadian air date in the first post, with the tacit understanding that the Canadians on the boards will discuss it after it airs there. That way, anyone who sees it later knows when to stop reading.
3) All posts on the episode are in spoilers until a certain time. My preference would be after the West Coast feed ends, which would be 10pm PST, or 1am EST. That way it's fair for all. After that time, no more spoiler tags are needed, and people should assume there will be free talk about the episode.
I'm a fan of option two. To my knowledge, there has never been any significant discussion or much discussion at all, on any of these threads before the episode has aired. They are, in effect, reaction threads. Therefore, I don't really see any reason why people would be reading the thread before the episode aired.