You can get the 2016 census data for Census Divisions (counties) here:
https://tinyurl.com/jn4y5zyn
If 25% of a county commutes to central counties, it's part of the MSA.
Toronto-Mississauga-Hamilton MSA
Core counties:
Toronto 2,988,408
Durham 711,426
York 1,200,262
Peel 1,563,641
Halton 610,581
Hamilton 581,722
Outlying counties:
Dufferin 68,347
Kawartha Lakes 81,042
Total population (2020 estimate): 7,805,429