Companies catalogue
- O'Sullivan Collision Services, Hamilton
- OBFT Oakville Boxing & Functional Training, Oakville
- OMS International - Canada, Burlington
- ONEC Engineering, Edmonton
- ONEC Engineering, Edmonton
- OWN Energy, Edmonton
- Oak-Park, Hamilton
- Oaklee Project Management and General Contracting Inc, Oakville
- Oakville & Milton Humane Society, Oakville
- Oakville Moving Company : ( Local Movers ), Oakville
- Oakville North-Burlington Federal Liberal Association, Burlington
- Oakville Parent - Child Centre, Oakville
- Oakville Performance & Wellness, Oakville
- Oakville Players, Oakville
- Oakville Preparatory Svc, Burlington
- Oakville Senior Citizens Residence (OSCR), Oakville
- Oakville Truck And Trailer Repairs, Oakville
- Oakville Truck/Trailer Repair, Oakville
- Oasis Engineering, Edmonton
- Oasis World Trading Inc., Hamilton
- Oaza Shawarma Plus, Mississauga
- Ocean Ontario Towing, Hamilton
- Ohso Fitness, Hamilton
- Oil Country Engineering Ltd., Edmonton
- Okimi's Limited, Smithville
- Old Abbey Park, Oakville
- Old Lawson House Eatery & Pub (The), Hagersville
- Olive Grove School, Mississauga
- Omagh Bible School, Milton
- Omar's Engineering, Edmonton
- Omnisource Corporation, Burlington
- On A Bun, Oakville
- On the Run, Burlington
- OnCourse Education, Hamilton
- Oneida Central Public School, Caledonia
- Onkar Travel, Hamilton
- Ontario Auto & Truck, Grimsby
- Ontario Driver & Vehicle Lcnc, Hamilton
- Ontario Osteopathic & Rehab, Burlington
- Ontario Rubber Industries, Brantford
- Ontario Towing & Recovery, Hamilton
- Ontario Works, Toronto
- Oodenawi Public School, Oakville
- Orbis Engineering Field Services Ltd., Edmonton
- Original Pizza, Hamilton
- Ortho World, Mississauga
- Oscar Peterson Public School, Mississauga
- Our Lady of Mercy Elementary School, Mississauga
- Overbeeke Postpiles, Pelham