Final answer:
Sir John A. Macdonald was the first Prime Minister of Canada, appointed in 1867 after the unification of several provinces into the Dominion of Canada.
Step-by-step explanation:
The first Prime Minister of Canada was Sir John A. Macdonald. He became the inaugural Prime Minister in 1867, following the formation of the Dominion of Canada by the British North America Act, which united Quebec, Nova Scotia, Ontario, and New Brunswick into one nation. Sir John A. Macdonald played a significant role in the nation's early development, including the expansion of its territory and the completion of the Canadian Pacific Railroad, facilitating the entry of Manitoba, Prince Edward Island, and British Columbia into the Dominion of Canada.