The premier, who is being put in a hell of a pickle, could always just tell Torontonians that the choice is theirs.
The could hold a binding plebisite for the entire GTA desrcibing EXACTLY what the taxes are, where the money will be spent, and EXACT timetable of each project..........no extensions. This would relieve the premier of having to make the decision for Torontonians and pay for it at the polls.
She can, quite fairly, that the choice is up to Toronto and if they refuse the tolls there will be no further funds coming from Queen's Park except the ones already underway. In other words, the money that has been announced stays but no further funds at all including after Eglinton is done, after that you are on your own. She can also freeze the operational support for the TTC/Metrolinx at current levels for at least 10 years.
She can legitimately say that the choice is up to you and what you decide you will live with for good or ill but the people of Ontario are not going to be on the hook for all Toronto's transit needs. If the GTA approves then great but if it is voted down she can turn to Metrolinx, when they inevitably ask for more money, don't come crying to us, you made your choice now live with it.
She is the premier of the entire province and is responsible to all the citizens {and tax payers} of Ontario and not just the annoited of Toronto. Despite Toronto believing that Ontario is simply a hinterland the reality is that the entire GTA still makes up less than half the province's population.