The problem with picking the perfect size for a city is that there is no perfect size. Some issues, like rapid transit, need to be dealt with on a large scale. Other issues, like local zoning standards, need to be dealt with on a much smaller scale. The trick to picking the best size is to maximize the number of issues that can be appropriately dealt with and making your city that size. Having two or more levels of government, each with specific responsibilities, can give a community two or more separate scales at which to operate. The problem with Toronto at its current size is that it is too large for local issues and too small for regional issues. It is however just the right size for many services like policing and fire protection.
Personally, I think dissolving the local municipalities in favour on one Toronto in 1998 was a mistake. They should have dissolved Metro Toronto, York, Durham and Peel, and made all the urban areas (those area that are now within the green belt) one large super region. They should have kept all the small local councils to deal with local issues and given all the large over-arching issues to the new super regional government. A similar system could have been implemented for Hamilton, Wentworth and Halton.
