- Order-in-Council PC 1911-1324, 12 August 1911
- Ordre de Bon Temps
- Ordre de Jacques-Cartier
- Ordre du Canada
- Oregon Treaty
- Orest Semchishen
- Orff Approach
- Orford Arts Centre/Centre d'arts Orford
- Orford String Quartet
- Organ Building
- Organ composition
- Organ Music and Organ Building
- Organ playing and teaching
- Organic Agriculture
- Organized Crime in Canada
- Orienteering
- Origins of Ice Hockey
- Origins of Labour Day
- Orillia
- Oriole
