London is in southwestern Ontario, (hence The University of Western Ontarion! ) Ottawa and Kingston would be just southern Ontario.
But the trunk of the ‘elephant’ isn’t really the same region as the body, come down to it.
Also, the trunk part is referred to as the snow belt, as it’s located between numerous Great Lakes, it often gets hit hard with lake effect snow, which can come from either side. (Lake effect snow, is when very cold arctic air rushes down over as yet unfrozen Great Lakes, picking up lots of moisture which then dumps as tons of snow, once the air mass moves again over land!)
Through the 1970s, CHYR, broadcasting out of Leamington, used to refer to its region in weather reports and local news as “Canada’s Sun Parlour”. I don’t recall whether CKWW, out of Chatham, used the same phrase for the whole area south of a line drawn eastward from the northern shore of Lake St. Clair or whether it was limited to the area around Leamington and Point Pelee. (I don’t recall hearing it from CKLW out of Windsor, but they were always more oriented to the U.S. audience, anyway.)
In human-geographic terms the “Southwestern Ontario” moniker is pretty much the best name you could use. Ontario is an enormous thing, obviously, about as large as France and Germany combined, but its large population is very unevenly distributed, so everything is relative. Basically, Ontario is
Toronto,
Eastern Ontario,
Southwestern Ontario, and
Northern Ontario.
Toronto and its immediate environs are so enormous and influential it’s basically a place all its own, concerned wholly with its own welfare, much as New York City ignores the rest of the State of New York - but with the added fun fact that while NYC at least isn’t the capital of NYS, Toronto actually is the capital of Ontario. Toronto separates Southwestern Ontario from Eastern Ontario, which, despite being south of most of Ontario, is called Eastern Ontario by most of its residents since it is directly east of most of the people of Ontario. Northern Ontario, which can be loosely described as Sudbury/North Bay and up, though Northern Ontarians will themselves distinguish the Sudbury/NB band from points further north, is so wildly different from the southern parts of the province in almost every respect that people have seriously talked about it becoming its own province, or maybe having the northwestern portion join Manitoba.
This is a simplification, of course - Ottawa is its own little world too, in many ways, being the nation’s capital and all.