I was recently reading the comic "The League o Extraordinary Gentlemen"(I'd recommend it to anyone into Steampunk, a really good one) and in it, one of the things that I found interesting, if secondary, was that instead of a Channel Tunnel, there was a gigantic bridge bwpetween Calais and Dover; If I'm being quite honest I don't know whether that's even mechanically feasible. Could it have happened? Was there, at any point, anyone pushing for something like that?
On a wider note, are there any other grand Infrastructure projects, after the end of the 17th century, that could have been implemented but weren't? How about the, probably infamous, suggested bridge to link Sicily to the Italian mainland? More canals and earlier canals? On that note I seem to recall having read about proposals to build a canal that would link the Great Lakes with the Atlantic through Quebec. Could more canals, in, say, Russia(Black to Caspian?) mean easier transportation, before the railroads or even at the same time as railroad construction was going on?