Update: Canal is almost half-way worked through on the largest stretch.
Due to the height of the terrain and the max slope of 300, we've had to add 1 more tile on each side of the project. The highway on the Southern edge will be moved one tile south to accomodate this. The plan is run a highway on the northern edge of the canal too.
I will post when to expect the Western highway to be out of service and replaced by a bridge.
First canal bridge span (1 x 16.) These will be placed approx every 20 - 24 tiles. A highway will run along the canal along the Northern Edge, in parallel to the highway on the South Edge of the canal.