Some good info links http://www.ontrmuseum.org/ http://www.rcaca.org/includes/index.asp http://www.warmuseum.ca/cwm/cwme.asp http://www.rcafmuseum.on.ca/(restored Halifax bomber)
Yon second link includes the information: "The first Centurions were equipped with the 17 pr "Firefly" gun which had been developed from a naval gun for adaptation to the Shermans (see Corps History p. 242)" Hmm... :-?