| Atomic Crayon | British Columbia |
| Atomic Energy of Canada Ltd | |
| Atomic IT | |
| Atomic Motion | Ontario |
| Atomic Motion | |
| Atomic X | |
| AtomicX | Ontario |
| Atomlabs Digital Marketing | Ontario |
| AtomVie Global Radiopharma | |
| Atoom ERP | |
| Atorvia Health Technologies | |
| Atout Recrutement | |
| Atrema Technologies | Alberta |
| Atrium Digital, Inc. | Alberta |
| Atrosoft Multimedia | Quebec |
| ATS Automation Tooling Systems, Inc. | Ontario |
| ATS Canada | Ontario |
| ATS Computer Systems | Ontario |
| ATSi Robotics | Ontario |
| Atsoft | Ontario |
| Atsoft Consulting | Ontario |
| Attabotics, Inc. | |
| Attain Solutions, Inc. | Alberta |
| Attendease Software Corporation | British Columbia |
| Attract | |
| AttriX Technologies, Inc. | Quebec |
| Atum Corporation | Ontario |
| Atvent Solutions, Inc. | Quebec |
| Atwood Consulting | Ontario |
| Atwood Technology, Inc. | New Brunswick |
| ATYS Informatique | Quebec |
| AU-PC Informatique | Quebec |
| Au-Zone Ltd | Alberta |
| Aucerna | Alberta |
| AUCO Marketing | |
| Audace Marketing | Quebec |
| Audatex Canada ULC | |
| Audcomp Group, Inc. | Ontario |
| Audera Acoustics, Inc. | Ontario |
| Audesse | |
| AudienceView Ticketing Corporation | Ontario |
| Audio Video Unlimited | British Columbia |
| Audiokinetic, Inc. | |
| Audiotek | New Brunswick |
| Audrey Hénault | |
| Aufait Web Design | Ontario |
| Augmented Reality Innovations | |
| Augurex Life Sciences Corporation | British Columbia |
| August Eletronics, Inc. | Alberta |
| Augustica Technologies, Inc. | Ontario |