Nicaragua Canal

This does not look like a pipe dream, but it could be quite a challenge.  There's a river that drains Lake Nicaragua into the Caribbean.  Thus, the waterway for most of the route already exists.  It is a matter of deepening it and widening it.

The hardest part may be the Pacific Ocean to the lake, which would require a ship to be lifted up to the level of the lake, which is nearly 100 feet above sea level.  It would have to traverse a narrow isthmus that is higher than this.  The lowest point of the isthmus is 184 feet.

Bottom line:

It would require a massive excavation of the isthmus at Rivas, in my estimation.  The rest would also be a massive dredging out of the San Juan River which flows to the Caribbean.

Funding of the project may not be quite so far-fetched.  There's a lot of money that could be made with such a project.  The company is said to not have any connection to the Chinese government.  It would appear to be a private venture.