Since downtown T.O was posted, I'll do the same for Montreal (although data is lacking compared to other cities)
Downtown Montreal: 17km^2
Population
1966: 136,600
1990: 82,700
2006: ~94,000
2011: 100,000
2016: Estimated 120,000
Source:
https://ocpm.qc.ca/sites/ocpm.qc.ca/...ille_final.pdf