Riverdale Park in Toronto looks very nice, but it was originally built in 1880 and has actually lost land due to highway construction and a landfill in the 1920s. And there is the rub with greenspaces. Short of building a park on landfill in water, what cities have is what they have. Land that is valuable as real estate or for commercial purposes will be kept that way.

Westchester County which is in the NYC metropolitan area was actually the first community developed as an affluent suburb in World history. First there were railroads and then the Bronx River Parkway which was the first automobile only highway built, from Manhattan to those big grass yards and white picket fences. The population density in Westchester County is 2,000/sq. mile vs. 75,000/sq. mile in Manahattan, but let's not make believe that they are seperate from each other. People working in Manhattan that want space and greenery to live in can get all they want if they have the money, and a nice foriegn luxury car.