Can you have a "southern" part of Alaska, or England or Scotland?
Actually when you leave Detroit to go to Windsor, and cross the bridge, you are headed south(South Southeast to be exact). Seattle is farther north than Toronto.
You've seen a small corner of a huge province. There is no set line for Southern Ontario - though the government does distinguish Northern from Southern by electoral district - northern districts getting some tax breaks and being eligible for certain economic development programs. Generally south of Lake Simcoe or highway 17 is "south".
The big difference is southern Ontario(or more correctly South West Ontario) has 80% of the population, is heavily industrialized. Northern Ontario is resource based -lumber, mining etc.
Ottawa is kinda half way - some parts are more like the north, others more like the south. Its in the Canadian shield so lots of rocks and pine trees which is not typical of South Western Ontario.
Toronto actually has the most northern tip of a "southern" ecosystem called Black Oak Savannah. It can be seen in High Park.
Its about 200 miles north of Toronto until you get to any real wilderness. Its only slightly farther to Wheeling West Virginia from Toronto than it is from Toronto to Ottawa, and Thunder Bay is twice as far to get to as Wheeling.
As for copyrights I am only half kidding. There was a recent dispute regarding a whisky maker in Cape Breton Nova Scotia, who labels a whisky Glen Breton. The scottish whisky distillers association is suing claiming that the Cape Breton distillers can't use the word Glen. You can't stick a pin in a map of Nova Scotia without hitting a Glen - its the word Valley in Gaelic, and there are glens everywhere, including the glen where the distillery resides and names itself after.
Anyway the vast majority of Ontarians consider themselves "Southern" Ontarians and we live south of the states of Washington, Montana and North Dakota. Toronto is 43 degrees North, and Northern California's border is about 41 degrees North.
I have to say that this week, after a freak cold snap, I wish I was in the US "South" instead of Southern Ontario.
James