Your facts are actually reversed. Gasoline taxes are paid by all of Ontario, including Toronto, and pay for the highways that run to every town / city in the province other than Toronto. The DVP and Gardiner, which are the toll roads in question are maintained entirely by the city of Toronto. 
In other words, the highway to Sarnia is subsidized by Toronto but the highways to Toronto are not subsidized by Sarnia. 
We are facing a $1B + repair bill on the Gardiner alone while half the cars on it do not contribute a dime . Tolls are a fair way to charge those who wear out the infrastructure.
Also keep in mind your sister paid $16,000 in Toronto land transfer tax.