I'm going to try not to be snide, but... 1812 was all about taking Canada. Cuba was an obsession for Americans in the 1890s, and when they lost in '56 they spent the next 20 years plotting revenge very poorly to get it back. You did want them and in the case of Canada, very badly; you just weren't able to.
few in the US wanted Canada or Cuba or all of OR, but most of the country wanted New Orleans. As for Cuba, we had a chance to take it as a colony after the SAW, but balked (luckily).
Actually, no. It's not American exceptionalism you're right, and it's not destined to happen. I'll agree there's a good chance it will, but it's not like there was this inertia pushing the U.S. further and further westward. The Louisiana Purchase changed U.S. history forever because this westward motion became a reality. In 1803 though the US was a small, developing largely immigrant nation that managed to expel the British with significant foreign aid. If Britain or France decided they
really wanted to press a claim on Louisiana, they could do it. They didn't though because at the time it wasn't worth the trouble, but it was well within their power. Likewise, if the US rejected buying the land (which was incredibly controversial at the time) I can't see them settling it very easy. New Orleans is something they wanted but if it was denied to them they'd end up just building up another port on the east coast.
See; (filler)New Orleans and most of the southern portions of the Purchase are going to fall to the US one way or another. It's not American exceptionalism to say that no other power in the region had the population, position, will or might to take it, all or in part, before the US. The Canadian-British might get the Dakotas, but that's about it. France or Spain certainly isn't going to get to hold onto the territory that's only nominally theirs to begin with.
As for the Texas argument; that American settlers will inevitably colonize new territories and bring them into its glorious democratic fold, Canada refutes just about everything mentioned so far. I'm Canadian, born and raised, my dad's side from India and my mom's side from Sask. My mom's grandma? From America! They came because of free-land and minimal administration. Could give less of two shits whose flag they were flying. From anecdotal quotes from my grandma to the books I've read, that seems to have largely been the case in the settlement of the US. A lot of Canada's early settlement in Nova Scotia, Ontario, the Prarie provinces and B.C. came from settlers in the US. Lots of settlers in the US came in through Canada. It's basically moot point until you get to the 1900s+.
It wasn't inevitable at all. Likely, but not inevitable.