In my 1812 timeline, The Eagle and the Lion, the UK brutally wins the war of 1812. Taking the modern states of Michigan and Wisconsin, forcing the US to "legally" purchase the Louisiana purchase and imposing other strict actions. The US in return aids the Patriots in the Upper and Lower Canadian 1837 rebellions, leading to a longer rebellion [but still a British Victory]. These rapid defeats sends a deep sense of isolationism into the US, and the Mexican American War is delayed, leading to a Mexican gold rush. Eventually this war does happen, but it is longer and has harsher terms for mexico, including the establishment of buffer states; The Mexican Republic of the North [Or Republica Mexicana del Norte] and the Republic of the Rio Grande.
I've concluded that the American Civil War would still happen, but I cannot figure out who would win. The South will have a larger population compared to OTL, more competent Generals, as well as likely support from the British and French. However, the North will still have the advantages it did in OTL.
I'm kind of stuck here and was hoping for an opinion.