Ground distance is not really relevant, it is all about air distance. The position of the jetstream in winter does make westbound flights across the Atlantic much longer (already we are seeing some 10.5 hr+ flights from the UK to Florida, where 9 hours is more typical in the Summer).
The opposite works in reverse of course (had a friend who went SFB-MAN in 6.5 hours in an A330 having taken over 10 hours on the outbound flight).
In the Summer the jetstream is usually way further north and although the flights still fight westerlies they are not nearly as strong.
If the strong winds can be avoided on the day in question the flight may only make one stop, and there is a good chance that the YYZ-LGW will be non-stop riding the jetstream home.
Flew an Air 2000 763 LGW-SFB-PVR-SFB-LGW route in October and on the return we went direct PVR-LGW (no stop at SFB) due to the strong winds. Flight time was just over 9 hours which is very good considering the 5,000nm ground distance between the cities.
But that's the difference between air distance and ground distance. The aircraft doesn't fly relative to the ground below it, only to the air around it.