I know the canal pretty well. I would assume it is a stream from the beginning. It was made deeper and wider (at some places) to be able to transport logs on the water.
"channelised=yes" would unfortunately not be suitable since there is no hard sides, except for under the bridge. Crossing the lake I would describe it as a flowline and in the north a small river. But it is man made and therefore a "canal".

Not an easy one to map for the renderer without stepping to far away from the acceptable. Do you get any ideas from my description of the canal?