For Toronto.
Toronto had stopped annexations before WWI. In the 1920s, raw growth of the suburban municipalities began to match that of the city proper.
The City of Toronto south of St. Clair Ave. was pretty much built out by 1920. North Toronto, the last early 20th century annexation (1912) filled up in the 1920s, and the City (35 square miles) was pretty much built out by 1930.
1921
City of Toronto 521,893
Suburban municipalities 89,550
Metro total 611,443
In city 85.4%
1931
City of Toronto 631,207
Suburban municipalities 187,141
Metro total 818,348
In city 77.1%
1941
City of Toronto 667,457
Suburban municipalities 242,471
Metro total 909,928
In city 73.3%
https://southofbloorstreet.blogspot....ropolitan.html
In 1920, York Township (population 57,448) surrounded the city to the north, northeast and west and contained the majority of the suburban population. The southern part was urbanizing while northern parts were rural.
Etobicoke Township 10,443
Leaside 325
Mimico 3,751
New Toronto 20,682
Scarborough Township 11,746
Weston 3,116
York Township 57,448
In the 1920s, several new communities were incorporated, mostly out of York Township. The more rural North York was split off from the urbanized south around Eglinton Avenue (Cedarvale, Oakwood, Mount Dennis etc.). East York to the northeast was split off as well. Forest Hill and Swansea were incorporated in the 1920s. A third western lakeshore suburb, Long Branch, was also incorporated.
By 1930, there were 13 municipalities in the Toronto metropolitan area. They all joined the Metropolitan Toronto federation in 1953, and the map held out until 1967:
https://www.researchgate.net/figure/...fig2_228354503
1931 population
East York Township 36,080
Etobicoke Township 13,769
Forest Hill 5,207
Leaside 938
Long Branch 3,962
Mimico 6,800
New Toronto 7,146
Scarborough Township 20,682
Swansea 5,031
Weston 4,723
York Township 69,593
One interesting to note is that the "favored quarter" North Toronto ended up in the city, while the working class fringe was left out. York and East York, which suffered enormously in the depression applied for annexation in the 1930s, but were turned down.
There's also a change in the 1930s and 1940s. Before 1930, the suburbs were actually more blue collar than the city. But in the 1930s and 1940s, affluent Forest Hill, Leaside and the Kingsway area of Etobicoke grew significantly and by 1951, the city was more blue collar.
1941 population
East York Township 41,021
Etobicoke Township 18,973
Forest Hill 11,757
Leaside 6,183
Long Branch 5,172
Mimico 8,070
New Toronto 9,504
North York Township 22,908
Scarborough Township 24,303
Swansea 6,988
Weston 5,740
York Township 81,052