Kaptin Kurk
Banned
If war between the US and Great Britain lasts for more than a year then Canada is swamped. Canada's population, relative lack of military industry compared to the Union, and long supply lines to Britain and more professional troops means by the law of numbers alone the Union can get more soldiers and equipment into Canada faster than the British can stop them or effectively defend against. It would delay major Union action against the South but not by enough to save the CSA.
That's also assuming no one in Europe decides to take advantage of the Anglo-French distraction. The Union had some pretty good relations with the Russian Empire at the time along with other possibilities so there's nothing stopping Lincoln from reaching out to Europe for allies to open a second front or shortage of grievances to motivate intervening. This won't hurt Britain as much but France is going to have to choose between winning the war in North America and losing in the metropole or letting the CSA go twist in the wind while holding off whatever continental allies emerge.
Not to mention a lot of Canadians at this time are transplanted Americans, who would probably not be all that upset at seeing the Stars n Stripes marching by.