Based on what you describe, I don’t see any legal ramifications. It’s pretty straightforward. An employee doesn’t have one of the essential qualifications of the job. There’s no indication that he belongs to any of the protected groups under human rights laws–age, disability, sex, race, religion, etc. And even if he was, a strong case can be made that having a driver’s licence is a bona fide occupational requirement for the position.
Other potential pitfalls to consider: Would firing the employee violate the terms of any contractual agreement or a collective agreement? Did you make any promises to the employee that he wouldn’t be fired for not having a driver’s licence? Barring any of these things–and they seem like remote possibilities–you should be good to go. Hope that helps. Glenn