Who is head of state of Canada federal government?

The head of Government for Canada is officially the Queen, but her power is mainly that of a figurehead. Her representative in Canada is the Governor General, which in turn appoints the Prime Minister, who is deemed as the person best able to command a majority of House of Commons votes (basically, the leader of whatever party won the election).

The present PM is the Right Honourable Stephen Harper(member of the Commons for Calgary Southwest), appointed by Her Excellency the Right Honourable Michaëlle Jean.