Bretwalda, those are some great ideas! They are all what I would want in the game regarding canals.
I remember emailing suggestions about canals before PTW came out, but it was a little late. Will they look as these suggestions, or have they looked at these suggestions? (as you can see I am a little new here) Will this discussion eventually lead to them implemented?
Just a few things I would like to suggest:
* I think canals should be built on any terrain, it should just take longer for hills and mountains and such.
* The worker being consumed upon construction of a canal tile is very appropriate considering all the lives lost in the creating of the Panama Canal
* Canals should boost trade (commerce) and be given a culture value as well. Also, civs would have to be nice to be allowed entry, makes the diplo game as well as the naval aspect MUCH more interesting!
* Maybe canals should have to go through a city's radius or connect the central square....we can debate that. At least it would need to be under one cultural influence as suggested. Or the canal could be like a small wonder....maybe by building the wonder, it could become easier to build other canals.....have special canal workers?
* Canals should have a limit: Either to connect water tiles from up to 4 or 5 tiles away, or maybe only on top of where rivers exist. So the tile itself would not have the canal, but the canal would exist in between, much like the rivers are shown.
I prefer the former, since the Panama and Welland and Suez Canals are that type.
EDIT: I was just thinking, that the chunnels or huge one tile bridges could be essentially the same thing, just from land to land across a small strait of land.