Nicaragua would be a sea level canal, no locks, but a much longer slog.
You probably know more than I do about it, but I know somehow they're tying it into the end of Lake Nicaragua and on a (now) small tributary that eventually runs either to Caribe or Pacific (it's how bull sharks migrate into fresh water Lake Nicaragua). I'm going to Granada on the Lake in November for a few days - nothing related to the canal proposal, but I may stumble into some information.