The government needs to spend something like $45 billion for public transit improvements to deal with growth and congestion in the GTA.
This public transit will take decades to build, cost a lot to operate requiring ongoing subsidies, and population growth in th emeantime means that congestion will get worse even with the new transit.
The greenbelt limits sprawl - but this limit on land supply also increases land prices, making the GTA less attractive for businesses.
Meanwhile, unlike the GTA, many cities in Ontario can easily handle population growth because they have infrastructure in place already and do not need massive and expensive infrastructure projects like subways or LRTs.
Housing in Toronto is expensive, and people live in poverty partly because of the high cost of housing. Obviously the GTA needs jobs too, but in some cases, we might be better trying to encourage new immigrants to settle outside the GTA.
Windsor, St. Thomas, The Niagara peninsula are well located but have lost industry in recent years - we need to shift jobs and people to these cities which are well located for trade with the US and can easily grow with little cost to the government for transit.