The Prime Ministers position and responsibilities are NOT defined in any statute of constitutional document (Canadian Encyclopedia, p.1894). The roll of the Prime Minister is largely based on the British Constitution.
To become the prime minister this individual must first assume the leadership of a national party. This person should be able to conciliate competing factions within the party and cabinet. The prime minister also should be able to delegate authority without loosing control and must be wary of offending various regions the country. Then the party must be elected by attaining the most seats in the House of Commons. "The powers of the Prime Minister are very great. "The functions of and duties of a Prime Minister in Parliament are supreme in their importance." says Arthur Meighen. The Prime Minister's power has been increasing over time, and the office now controls much of the power of the Canadian government. For example, the Cabinet is briefed on the budget, but the Prime Minister and the minister of finance actually make all major budgetary decisions. The Prime Minister can also act at will as the chief spokesperson for the government on any policy issue. Policy statements made by the Prime Minister become by default a government policy. As shown here a Prime Minister has much power over government. A majority government might be known as a prime ministerial government and not a democracy because of the power that the prime minister has over his/her cabinet and ministers.
One of the Prime Ministers powers is to appoint, reshuffle or dismiss ministers. A cabinet shuffle, (also called a reshuffle) involves the movement of a set of cabinet ministers by the Prime Minister. The power to dismiss or reshuffle exerts a substantial influence over the cabinet. This usually determines the collective decision of the cabinet without a formal vote taking place. The Prime Minister holds this principal position with the support of his cabinet.