London is about a 3 hour drive south of Toronto.
So temperatures vary a bit due to distance, but not drastically.
That being said, London is in southern Ontario's 'snow belt region and subject to Lake Effect snowfall in ways that Toronto isn't.
-Prevailing winter winds off Lake Huron pick up moisture and dump it inland.
London's inside that area. Toronto isn't.
Two years ago, London got hammered hard by a good ol' fashioned blizzard:
Link - http://nimg.sulekha.com/others/original700/canada-snowstorm-2010-12-7-16-50-0.jpg
Link - http://www.ctvnews.ca/near-emergency-level-snowfall-in-london-ont-1.582707
Link - http://www.theweathernetwork.com/news/storm_watch_stories3&stormfile=one_year_ago_looking_back_a_051211
By comparison, Toronto got just a dusting barely enough to cover the grass:
Link - http://www.youtube.com/watch?v=bz_WUlgXm2w
So which city is better to live in depends on how much you like snow.
Toronto never gets as much snow as snow belt communities like London does.