The silent Canadian stations continue to be "notified" to the FCC through the normal diplomatic channels, just as if they still existed. On occasion, these operations are resurrected under new ownership -- for example, the 690/940 Montreal facilities Chris mentions.
(this includes not only the Class A stations which, as David says, belong to Canada and not to the specific station -- but also the Class B, C, and D operations. Not that there was ever more than a literal handful of Class D stations in Canada... to my recollection, today there's only one left)