What is the difference between the oppression remedy and a derivative action in an Ontario corporation?

These are two different tools under the OBCA (the CBCA has similar provisions) that address different kinds of harm. The oppression remedy lets a shareholder, or certain other qualifying stakeholders, ask a court for relief where the corporation's or directors' conduct has been oppressive, unfairly prejudicial, or unfairly disregards that person's interests — it is personal to the complainant, addressing harm to them specifically, such as being frozen out of decisions or having their shares diluted unfairly.

A derivative action, by contrast, is brought on behalf of the corporation itself for harm done to the corporation, such as a director breaching a fiduciary duty and causing the company financial loss, where the corporation would normally have to sue but its own management will not, often because the wrongdoer controls the board. Because a derivative action is brought on the corporation's behalf, any recovery generally goes to the corporation, not the individual shareholder, whereas an oppression remedy can result in relief tailored directly to the complainant, such as a share buyout. A derivative action also requires the shareholder to first obtain leave of the court, while an oppression claim generally does not have that same preliminary hurdle.