Could the United States plausibly got all of the Oregon Country? I mean ALL of the extreme American claim up to 54'40
Unlikely, but possible. The extreme 54'40 claim was more of a negotiating tactic than actual goal. However, if the border does not get resolved, it is possible that as more American settlers enter the region that some begin to occupy areas north of the 49th parallel which eventually forms the basis for a strong US claim to the region. However, much would depend on what happens during this time period as there would be many factors pushing both sides to agree on the 49th parallel as the border.
Once Texas entered the Union, there was going to be a reaction to secure more land in the north, which is where the 54'40 claim came in. And once Texas was in the Union, you were risking war with Mexico because of the Rio Grande/Nueces dispute and that the US wanted at least some of California to include San Francisco bay. So the US is in danger of two wars at the same time. In that regard, a peaceful resolution with MX (they agree to the Rio Grande border and sell some of California), might encourage a more bellicose stand with Britain, or at least a desire to not rush the Oregon border dispute. The next step would either be a victorious war against Britain in 1848 (very risky) or more US settlement in the area and a future border crisis when the US is much stronger (1860? 1880?).
Aside from Vancouver Island, which Britain will fight to keep, sure. The longer the joint-management arrangement continues without it being settled, the more it's going to favor the USA. Heck, British Colombia seriously considered joining the USA in 1867.
Heck, British Colombia seriously considered joining the USA in 1867.
I think people overestimate what the dispute was over. Aside from jingoist election speeches, the US was not pushing aggressively for the entire territory. Most of the dispute centered on the so-called Oregon Triangle, which was basically the territory north of the Columbia River that juts out. What did the US want with the entire thing, after all?
The majority of people in BC preferred to join Canada.
The sacrifice for Oregon is that the US has no claims west of the Rio Grande and south of the 32nd parallel (the likely boundary of any deal with Mexico). Since the US has no claims to that area at all, there will be no war with Mexico as there will be no dispute that provides a casus belli. The only way the US might possibly posses that land is if Mexico seeks to sell it for more cash, which is dubious but still possible, later on.
That is a pretty hard proposition to back up. There was little interest in joining the US or the Canadians. While it would be fair to say that there was greater interest in joining confederation than being annexed by the US, the fact is that the vast majority of British Columbians wanted nothing to do with either. If you look at the outcomes of the election immediately prior to the Yale Declaration, the confederation league failed to elect a single candidate to the BC Parliament.
The reality is that British Columbia was ordered into confederation, they really had no interest in joining with either the US or the Canadians.