Maybe
I'm curious to see what they have for Northern secessionist movements. I remember hearing that there was talk, during the War of 1812, of the Northern states seceding in protest over the decline in Atlantic trade due to British impedance.
I think it's possible that a war over Oregon would provoke much the same sentiments.
This probably won't happen....
Prior to 1812, there was more secessionist talk in the north than the south; most of the presidents at that time came from Virginia, and the Jefferson embargo devastated the shipping. But that was the high point, and shipping had never recovered to the same extent, as far as I am aware.
Also, the north's economic situation and the US's political arena had changed greatly by that time. The embargo itself encouraged the manufacturing which Jefferson disliked, and the 1840's and 1850's were when the north's resources were converted much more rapidly to railroads and industrialization than to shipping. True, they need plenty of places to ship those products, but that's where the south comes in...
The 1828 Tariff of Abominations had already enraged the south, and the 1832 compromise did not go far in mending relations ( nullfications and jackson ). As such, I can see a war with Canada and Britain being much more irritating to the south than the north: they'll absolutely HAVE to buy northern products, at any price. And to make up for the loss of overseas trade, I can definitely see northerners raising their prices drastically on the rural south.
Now, say you don't go to war with Mexico, try to avoid that Kansas mess.......
Much like the north called the Mexican-American war a "Southern plot" ( although that's not really true ), the south would undoubtably call a war with Canada a "northern plot". The addition of new territories strictly to the cold north would be outrageous; the south needed Texas and the other territories just to keep pace with the North's population and electorial majority. One reason that the civil war took place was that the south could not doubt that the north would win effective majority in the next five, ten years. Take ontario, quebec, etc, and they have no chance whatsoever by 1860.
As I see it, the north will probably not be the one to secede in any case, for the game starts too late.
But if anyone wants the south to win the civil war, I suggest starting it in 1850 >=)