Can an employer suspend me without pay without it being a constructive dismissal in Ontario?

Generally, no, unless the employment contract or a clear, established policy specifically allows for it. An employer that suspends an employee without pay, without a contractual or policy basis to do so, is generally treated as breaching a fundamental term of the employment relationship, which can amount to constructive dismissal in much the same way an unauthorized pay cut or demotion can.

Ontario courts have recognized that unpaid administrative suspensions, even where an employer believes it is acting reasonably, for example during an investigation into alleged misconduct, still generally require either the employee's agreement or a clear basis in the contract or an established policy, since simply withholding pay is not an inherent management right that exists absent that basis. A paid suspension while an investigation proceeds is generally viewed very differently and is much less likely to be treated as a constructive dismissal, since the core economic terms of employment continue uninterrupted during that period, even though the employee is temporarily kept away from the workplace.