South-western Ontario is mostly farmland, with a handful of communities that also have or had a manufacturing base. Guelph, which bounds south-western Ontario and the golden Horseshoe (Toronto, Hamilton etc.), has some people who commute into the GTA.
Guelph and Kitchener-Waterloo to the west of it have substantial light industry, so they took a hit, but they were diversified enough to come through quite well. Note that Guelph has been an agricultural college town for over a century, and Waterloo is one of the top computer and engineering universities in the world. In the centre of the region, London is the financial centre of the region, and its University of Western Ontario has the top business school in the country that holds its own on the international stage, and excellent medical and law schools, so it pulled through OK, although half an hour south of it, St. Thomas took a beating because it was mostly dependant on the auto industry (well, that and however much tourism one gets for being the place where Jumbo the Elephant was hit by a train). At the western end, across the river from Detroit, Windsor took a beating and is not out of the hole yet because it was almost entirely dependant upon the automotive industry, and notably its university is not so much outstanding in its field, but rather is more along the lines of out standing in a field.
IMHP, the region as a whole has come through OK because the region, the province and the country all put in a lot of resources over many years to develop its universities which in turn have generated a metric shit-ton of businesses, so when the automotive industry crashed, the cites in the region were well positioned to absorb such a huge hit and emerge scarred but surviving and in one case thriving.
Apart from the rust belt, I’ve seen the same sort of thing in north eastern Ontario’s Sudbury and northwestern Ontario’s Thunder Bay, where there have been ups and downs in the two primary industries, mining and forestry. Long-term development of these cities’ universities have helped stabilize and grow their economies. For example, the future in hard rock mining is in robotics and automation. Sudbury Laurentian University, in conjunction with the mining industry in its region, is the leader in this. Lakehead’s forestry programs are preparing the forestry industry (which will never recover from the move away from pulp and paper) for changes anticipated by global climate change.
IMHP, for the rust belt or other regions hit with a game changer, the key to rolling with the punches is to start with a regional centre and put in a lot of resources over the years into education, which better prepares the regional centre and much of the rest of the region to roll with the punches rather than be steamrolled flat by them.