http://en.wikipedia.org/wiki/Canada#Government_and_politics
Government and politics
Main articles: Government of Canada and Politics of Canada
A building with a central clocktower rising from a block
Parliament Hill in Canada's capital city, Ottawa
Canada has a parliamentary system within the context of a constitutional monarchy, the monarchy of Canada being the foundation of the executive, legislative, and judicial branches.[94][95][96][97] The sovereign is Queen Elizabeth II, who also serves as head of state of 15 other Commonwealth countries and each of Canada's ten provinces. As such, the Queen's representative, the Governor General of Canada (at present David Lloyd Johnston), carries out most of the federal royal duties in Canada.[98][99]
The direct participation of the royal and viceroyal figures in areas of governance is limited.[96][100][101] In practice, their use of the executive powers is directed by the Cabinet, a committee of ministers of the Crown responsible to the elected House of Commons and chosen and headed by the Prime Minister of Canada (at present Stephen Harper),[102] the head of government. The governor general or monarch may, though, in certain crisis situations exercise their power without ministerial advice.[100] To ensure the stability of government, the governor general will usually appoint as prime minister the person who is the current leader of the political party that can obtain the confidence of a plurality in the House of Commons.[103] The Prime Minister's Office (PMO) is thus one of the most powerful institutions in government, initiating most legislation for parliamentary approval and selecting for appointment by the Crown, besides the aforementioned, the governor general, lieutenant governors, senators, federal court judges, and heads of Crown corporations and government agencies.[100] The leader of the party with the second-most seats usually becomes the Leader of Her Majesty's Loyal Opposition (presently Thomas Mulcair) and is part of an adversarial parliamentary system intended to keep the government in check.