Caught him mention this here, decided to look up the project.
Seems neat. There's a few different routes that have been proposed over the years, changing with the political conditions I guess? Train gang will be fans of it.
For Bolivia I think the obvious merit is that it provides much more port access options for a landlocked country which is probably essential for maintaining their sovereignty.
The big agro-oligarchs, yes. It's way easier to be a colonial administrator than to be the leader/powerplayer/burocrat of a real country.
South America is what would have happened if the Confederacy had won the Yank Civil War.
In ~1816, while discussing with people who supported independency from Spain, José de San Martín said "yo we need more national industry ASAP" and the agrooligarchs and dipshits who controlled imports from Buenos Aires Port pissed and moaned saying that would enanger Europe. They didn't want independency, they wanted to keep being a colony but able to trade with whoever they wanted.
ALL Argentinian history is a repetition of that same pathethic scene. Decade after decade. And in every turn the agrooligarchs and port dipshits (then replaced by finance capital) won.