Okay, here's the thing - as we see in the second half of the film after Logan and Jessica have escaped, The Domed City is located within a day's walk of Washington D.C. Logan and Jessica were born and raised within The Domed City, as were all the other characters we meet there. Why do Logan and Jessica have English accents?!!?
English vs American English is a bit like widescreen vs pan & scan. You can speak American English, but the Queen's English is how it's meant to be heard.
Y'all were independent before thinking you could take over here... take over failed, thus the war the USA started, failed. I think that qualifies as the opposite of winning.
Manifest Destiny had nothing to do with Madison. Continentalism was first discussed by Adams, but wasn't in any way a policy of the US. You might be conflating the Monroe Doctrine, which was in partial response to the War of 1812, but happened a decade later under James Monroe, not James Madison. Manifest Destiny didn't became a political concept until 1845, and was coined by a journalist. US war with Canada had several causes, including trade embargos due to the Napoleonic Wars, impressment of US citizens on the high seas, British claim to board any American ship, and the arming of native americans by the British which led to several raids against US frontier towns. The US barely had a standing army then, and the militias weren't interested in expansion - especially as they were from the North East which were strongly Federalist and opposed the war. Neither side gained much during the war. The US lost its repeated invasions of Canada, Britain lost when it invaded NY state (with Canadians), and lost in its invasion of New Orleans. Indeed, the only major land trade that happened was when the US seized Indian lands that were a very large part of the British military plans. The Brits planned on creating a Native American entity to stop US expansion west, and that failed miserably.