I suspect "The Canal" is just a local name for it so keeping that as the name makes sense. To me "stream" suggests a natural feature whereas "ditch" suggests a man-made feature. There are a couple of useful photos here: https://www.geograph.org.uk/photo/609666 and https://www.geograph.org.uk/photo/5404500  
I was hoping someone with local knowledge might come back saying either "These were always streams and they have been straightened." or "These are entirely man-made for draining farmland." The former I'd call a "stream". The latter I'd call a "ditch".