Canada did not offically sdeclare war on Germany until 10th Septermber 1939 according to an Wikipedia page https://en.wikipedia.org/wiki/Decla...nd_World_War
The BNAPS War Times group news letter of May 2001 says that censorship did not start in Vancouver until 8th September.
I have just got a censored cover from Toronto to Holland cancelled at 09.30 am on the 4th September 1939. The censor, number 19, was based in Ottawa. Toronto did not have a censor station. Presumably it took at least one day to send the letter to Ottawa so the censorship would have been done after the 4th.
The obvious question is when did Canadian censorship on Ottawa start.
There are no other postal marking on the cover other than the original dater.