The correct answer is - the British monarch.
Even though there's no real power in the monarchy nowadays, its symbolism is still present as a historical authority. Canada is a country that has been formed by the British crown, and the foundation of the country and its legislature, councils, actions, have all been historically under the governance of the British monarchs.
Nowadays, Canada is a parliamentary democracy, and the monarchs do not have any influence in the country's politics, but symbolically, the current Queen of England, Queen Elizabeth II, is the official monarch that rules Canada.