agracier, which river/canal objects are you referring to here, mate?
In the map-maker, there is a section of objects titled 'Title CatPlate'.
While going through the objects a few days ago when populating a map, I chanced upon these. They are objects that are meant to stand in for rivers and canals. What is good about them is that the rivers and canal objects are much narrower than the game generated rivers and therefore much more realistic. There are for instance a few river objects that are very very narrow and give good simulations of a creek or arroyo.
The canal objects are also a good idea. They are straight as canals should be and also not too wide. The downside of the canal objects is their color: a very odd looking khaki-greenish color.
But the main drawback to using these river/canal objects is that they require flat terrain, otherwise you will see parts of them floating above ground. And several river objects are very long - a good idea in principle - but that makes it even harder to place them since seldom is the terrain flat enough to use them correctly.
I tried the canal objects out on a map I'm busy with, but the coloring was way too off and it was a big headache trying to find terrain flat enough.
But these objects are a good idea though.