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The Canadian constitution determines that the Commander-in-Chief of the Canadian Armed Forces is the country's sovereign, who, since 1904, has authorized his or her viceroy, the governor general, to exercise the duties ascribed to the post of Commander-in-Chief and to hold the associated title since 1905. All troop deployment and disposition orders, including declarations of war, fall within the royal prerogative and are issued as Orders in Council, which must be signed by either the monarch or governor general. Under the Westminster system's parliamentary customs and practices, however, the monarch and viceroy must generally follow the advice of his or her ministers in Cabinet, including the prime minister and minister of national defence, who are accountable to the elected House of Commons.

Who must sign these orders for them to be valid?
the monarch or governor general