 The Union Jack served as the formal flag for the various colonies of British North America, and remained as the formal flag of Canada after confederation.The Union Flag remained as Canada's official flag until 1965; although from late 19th century to 1965, the Canadian Red Ensign was also used as an informal flag of Canada.In 1964, the prime minister of Canada, Lester B. Pearson, introduced plans to replace the Union Flag with a new national flag, spurring the Great Canadian Flag Debate.