The Queen's representative in Canada. It's now largely a symbolic/ceremonial position but at one time it had significant power. However, the position technically still has some power (not sure if this has occurred ever?):

While the role of the Governor General is significantly restricted by conventions, it is not entirely symbolic.[13] On rare occasions, a Governor General can exercise personal discretion, meaning that he or she can act independently of prime ministerial advice. This ability to exercise personal discretion revolves around the Governor General’s “reserve powers.”[14] Two established reserve powers are the Governor General’s authority to refuse a prime minister’s request to dissolve Parliament and the right to appoint and dismiss a prime minister.[15]

https://www.constitutionalstudies.ca/2017/09/governor-general-of-canada-the-role-the-myth-the-legend/