Longer than 100km: 2 (0 in alpes)
Longer than 50km: 7 (0 in alpes)
Longer than 20km: 34 (3 in alpes, one of which is the CERN particle accellerator.)
Longer than 10km: more than 100
http://en.wikipedia.org/wiki/List_of_tunnels_by_length
The vast majority of these don't count.
A water supply system is not a road tunnel. And they're not similar engineering-wise; a water supply tunnel doesn't have to deal with exhaust systems, or fires, and can be much smaller.
A metro/subway system under a city (shallow distance underground, high value, cheaper to build, easy to access) is not a tunnel through a mountain chain.
You have to go 26 places down the list to get to a road tunnel!
Keep in mind as well; a 2-lane road tunnel (like many of these tunnels; 1 lane each way) is not exactly going to allow the same amount of traffic as an 8 lane superhighway between cities - and isn't going to allow you to ship large armies through it easily.
Look at the real world; are there tunnels through the Himalayas? The Rockies? The Pyrennes? the Andes? No, going through mountain ranges is a PITA, there are narrow roads through passes, or you go around.
Other than a few through the alps, building transport tunnels through big mountain chains is not something we do, because it would be hideously cost ineffective.
The Panama Canal was completed 1914, the Zues Canal in 1869. This is earlier, so you are correct there, but in terms of civ, its the modern area as well.
No, in terms of Civ, its the industrial era. There is a vast difference between mid 19th century (riflemen, cavalry) and end of the 20th century (stealth bombers). Remember that the game slows down, so that turns start being 1 year instead of 2 years or 4 or 50.
with bridges, you could be across the water and onto the other landmass in one turn
Why would this be a desirable gameplay feature? Water is supposed to be a barrier. Even the Chunnel doesn't connect England to the continent in the same way as if they were actually connected by land.