You are correct about the provinces getting discretion.

FWIW, on my machine (10.4.8) America/Montreal and America/Toronto both have the new date, while America/Vancouver does not. I know Quebec and Ontario are both going to use the new date, but I don't know about BC.

The zoneinfo may be correct if BC isn't switching to the new dates. If they are, somebody needs to tell Apple in the next couple of weeks.

Aside:
As if the switch wasn't boneheaded enough, the Canadian federal government had to leave it up to the provinces. Decentralization is fine and dandy, but applying it to something that needs national and even international standards to umm... you know... *work properly* is just plain stupid.

Well on this Mac (10.3.9) in America/Montreal, the date has not been updated. Did Apple only updated Tiger clients?

It would seem so. Other posts attached to this hint mention a 3rd-party patch available via AFP548 that should help in your situation.