Can we terminate someone with cause for harassment?

The short answer is potentially, but it depends on the circumstances. 

In most incidents of harassment, especially if they are isolated and there is no serious or lasting harm, terminating an employee with just cause for dismissal would be an unreasonable reaction. That does not mean, however, that an employee cannot be let go without cause. Employment can be terminated without cause at practically any time for practically any reason as long as an employee is paid reasonable notice. 

There are, however, incidents where termination for just cause may be appropriate. Serious incidents of violence or harassment where conduct is extreme may be justifiable by an employer to warrant just cause for dismissal. Similarly, employers can outline in their workplace policies that penalties for repeated discipline can include just cause for dismissal. Recent Ontario law however has shown that even in most just cause cases, employees will still be entitled to receive their minimum payments guaranteed under employment standards law.