Interesting question. It depends on the city. In many cases, suburban development was a natural extension of the existing urban form well into the 1950s and sometimes into the 1960s. It took awhile for Don Mills-style suburbia to catch on.
For example, Killarney, Vancouver was developed in the late 1950s, and it maintains the same kind of street grid and density as other, older areas:
https://maps.app.goo.gl/TztXab33JQxExEUS9
In Calgary, Rosscarrock was not developed until the late 1950s and it maintains a street grid with back alleys:
https://maps.app.goo.gl/LLQzkwAbihZqXDP37
Next door is Westgate, which developed just a few years later, but you can already start to see more Don Mills-style features in the planning:
https://maps.app.goo.gl/KmmduP7K3FqVX6Qk6
Montreal is an interesting case because you have examples of both Don Mills-style development and more urban typologies being built at exactly the same time.
Lakeside Heights, Pointe Claire, developed in the 1960s:
https://maps.app.goo.gl/pDvFh7VkyxHZtrbv7
Montreal North, also developed on greenfield land in the 1960s:
https://maps.app.goo.gl/FZAtYFtKo5uiL2y89
And then you have a very distinctive 1960s typology, which is triplexes developed on a car-oriented suburban street pattern. This is common in areas with strong Italian influence like St-Léonard, Anjou and LaSalle:
https://maps.app.goo.gl/aJTDPRPQEh9WTaZW8