| City | 2026 Pop. ↓ |
|---|---|
| Ottawa | 1,218,903 |
| Oakville | 248,459 |
| Oshawa | 221,497 |
| Orillia | 38,535 |
| Okotoks | 34,057 |
| Orangeville | 33,465 |
| Oro-Medonte | 24,947 |
| Owen Sound | 24,443 |
| Oak Bay | 18,668 |
| Olds | 9,734 |
| Otterburn Park | 9,684 |
| Oromocto | 9,482 |
| Otonabee-South Monaghan | 8,296 |
| Oliver Paipoonge | 6,591 |
| Orford | 5,886 |
| Osoyoos | 5,743 |
| Oliver | 5,263 |
| Oka | 4,392 |
| Ormstown | 4,354 |
| Okanagan-Similkameen C | 4,123 |
| Okanagan-Similkameen D | 3,984 |
| Opportunity No. 17 | 3,614 |
| Okanagan (Part) 1 (IRI), North Okanagan | 3,533 |
| O'Leary | 2,935 |
| Outlook | 2,685 |
| Okanagan-Similkameen A | 2,486 |
| Okanagan-Similkameen G | 2,419 |
| Okanagan-Similkameen H | 2,393 |
| Okanagan-Similkameen I | 2,371 |
| Oxford House 24 | 2,254 |
| Obedjiwan 28 | 2,164 |
| Opaskwayak Cree Nation 21E | 2,159 |
| Okanagan-Similkameen F | 2,156 |
| Okanagan-Similkameen E | 2,092 |
| One Hundred Mile House | 2,039 |
| Orkney No. 244 | 1,965 |
| Oakland-Wawanesa | 1,883 |
| Oakview | 1,672 |
| Oneida 41 | 1,608 |
| Osler | 1,516 |
| Osoyoos 1 | 1,503 |
| Oxbow | 1,282 |
| Oxford | 1,270 |
| Okanagan-Similkameen B | 1,199 |