Can an Ontario professional corporation have shareholders who practice different professions?

Generally, no — most Ontario professional corporations are restricted to voting shareholders who are all licensed members of the same profession, since the certificate of authorization is issued by that profession's own governing body based on rules specific to it. A corporation authorized for one profession usually can't simply add a shareholder licensed in a different, unrelated profession and expect the existing permit to cover both.

There are narrower exceptions in some regulated sectors, particularly certain health professions, where governing legislation specifically permits defined multi-discipline arrangements between related professions under conditions set out in that framework. These are the exception rather than the default, and they don't extend automatically to any combination of professions someone might want to combine. If you're considering a multi-discipline structure — for example, professionals from two different regulated fields wanting to share ownership of one practice vehicle — check with both governing bodies involved before assuming it's possible, since one or both may require a different structure entirely, such as separate corporations that contract with each other rather than shared ownership.