Who does Manifest Destiny affect in British North America (Canada) and why does it affect them?
Manifest Destiny was an idea of American exceptionalism and white supremacy that dictated that Americans were destined to explore and expand their borders. This notion of continentalism also meant that America would annex British North America (or Canada) in order to oust the British from North America.
The policy of annexation (by divine right) affected the independent provinces of North America and, fearing invasion, they clubbed together in what is currently known as Canada. In 1867, provinces of Quebec, Ontorio, New Brunswick and Nova Scotia created the Dominion of Canada. Manitoba and British Columbia joined in 1870 and 1871, respectively to prevent any threat of US annexation. New territories were created (the District of Keewatin and the Yukon Territory) to expand and develop more land and allay people's fears. Alberta and Saskatchewan joined in 1905, completing Canada.
So while Manifest Destiny forced the independent provinces to club together, it led to the rise of a nation (Canada) and to their overall growth and protected them from annexation by the US.