Just picked this up from the MSE forums:
"Mail services to Canada suspended
Due to industrial action by Canadian postal workers all mail services to/from and within Canada have been suspended. Mail sent since Friday 10th June may not have been delivered and any mail currently in the Royal Mail system will be retained until service is resumed. From tomorrow, Thursday 16th June no further mail for Canada will be accepted until normal service resumes.
Further details can be found at the Canada Post website."