The USA believed in 1812 that overcoming British resistance would be easy. There were few British garrisons, and mostly farmers and merchants who were largely French, along with aboriginal peoples.
Canada’s apparent vulnerability—Jefferson had famously suggested that its conquest would be “a mere matter of marching” for American troops—made it an even more enticing target. (https://www.nps.gov/articles/why-canada.htm)
The USA failed in its military attempt due to heavy resistance from the Acadian, African descended, and Aboriginal populations. Why did these groups provide such unexpected resistance?