| OnSite I.T. | Alberta |
| Onsite Training | Ontario |
| OnSiteASAP | Quebec |
| Ontario Aerospace Council | Ontario |
| Ontario Bioscience Innovation Organization | |
| Ontario Brain Institute | |
| Ontario Centre for Education and Training | Ontario |
| Ontario Centre of Innovation | |
| Ontario Computer Works Ltd | Ontario |
| Ontario Creates | |
| Ontario Northland | Ontario |
| Ontario Nursing Informatics Group | Ontario |
| Ontario Power Generation | Ontario |
| Ontario Research and Innovation Optical Network | Ontario |
| Ontario Research Centre for Computer Algebra | Ontario |
| Ontario Science Centre | |
| Ontario Security Systems | Ontario |
| Ontario SEO | Ontario |
| Ontario Teachers' Pension Plan | |
| Ontario Tech University | Ontario |
| Ontario Tech University - Faculty of Business & IT | Ontario |
| Ontario Website Designer | Ontario |
| OntarioMD | Ontario |
| OntheMarkLocalMarketing.com | |
| Ontopical | |
| OnTrack Engineering | Alberta |
| Ontracks | Alberta |
| Ontrak Control Systems, Inc. | Ontario |
| Onward | Ontario |
| Onward Computer Systems | Ontario |
| Onware | Alberta |
| OnX Canada | Ontario |
| Onyris, Inc. | Quebec |
| OODA Technologies | Quebec |
| OOK Enterprises Ltd | British Columbia |
| Oolong Media | Quebec |
| Ooober | Ontario |
| Oops! Design | Alberta |
| Opacity Design Group | British Columbia |
| Opal Multimedia, Inc. | Quebec |
| Opal-RT Technologies, Inc. | Quebec |
| Opale.Net | Quebec |
| Opalux, Inc. | |
| OPAS Mobile | |
| OPC Training Institute | Alberta |
| OpCode Solutions | Quebec |
| Opcode Systems, Inc. | Ontario |
| Open Door Technology, Inc. | Alberta |
| Open Government | Ontario |
| Open Ocean Robotics | |