why did so many Americans going back to the Declaration of Independence and Revolution believe annexing Canada was a natural expectation

Many believed that annexing Canada was the next step because it was as well a British colony, as the thirteen colonies were before the Independence. They thought it would be a cakewalk and that Canadians were eager to shake the British off their back. During the 1812 war there was a march upon Canada, as the Americans engaged in war with the British and Canada was still a colony, but it didn't work out good for the Americans.