Is a new employee automatically subject to a probationary period?
No. If you want your new employee to go through a probationary period, then you should clearly state that in in the employment agreement.
The reason for having a probationary period is to help the parties determine whether a continued employment relationship is viable.
The typical probationary period is three months. While this is OK for lower level employees, you may want to have a longer probationary period for senior employees.
Subject to the minimum notice requirements of employment standards legislation, an employer can dismiss an employee without notice, or pay in lieu, during the probationary period.
However, the law requires an employer to act in good faith when it is making a decision about the suitability of the employee.