The Panama canal not only wiped hundreds of thousands' savings in France, it also triggered a massive scandal for the implication of a number of députés and what they knew and feigned to ignore, all the way up to the Presidency itself. It was the start of a strong antiparlementarian feeling in a large part of the population, some of which found a way to express itself soon after in the Dreyfus Affair.
Then there is the fate of the Southern Cone to consider. Up till 1914, they did very well for themselves, being mandatory waystations for ships going from the Atlantic to the Pacific, their standards of living were some of the highest in the world. Exports of beef continued to sustain Argentina during WWI, but I think after that the Panama canal opened , it meant growing irrelevancy, gradual and relative impoverishment, which led in turn to domestic troubles.
Some interesting ideas there- I was aware of the Tehuantepec concept before, but not the lower Panama ones.
As for the Missouri-Snake river case, I think that fails on just how un-navigable the Snake River is- pretty much all the Idaho stretch is rapids, waterfalls and gorges, to the extent that historically the steamboats only made it as far as Lewiston, or at most the lower Hells Canyon. Looks like even Boise is too far for that- particularly given the fact that there's a waterfall higher than Niagara Falls in the way.
Excellent article. There has been so much AH speculation about this that I struggled a bit to come up with something different for LTTW - probably just as well I hadn't heard of that ship rail or I'd have been tempted to do that!
(What I did in the end, for the uninitiated, is have a setup where two rival powers control Nicaragua and Panama, so what happens is they both simultaneously build a canal, and who finishes first becomes an ideological race like the Space Race in OTL).