Thanks, Squipdit Fashions and Imagegear. On the basis of what you've identified, it seems to be the Empress of France and, therefore, the return journey from Montreal to Liverpool in 1958.
Any necessary bunkering at Quebec or Halifax would have been an opportunity for a photo, light permitting, but I wonder if he would have still been wearing uniform at that point. (How times have changed!) I reckon Quebec might have taken around 10 hours' sailing from Montreal; Halifax a couple of days.