The canal cruise that we took was interesting in the beginning but after an hour, I got a bit bored. Our guide just steered the boat and played a prerecorded tape. My boyfriend on the other hand, fell asleep due to the beer at the Heineken factory earlier that day.
I would recommend taking a short one. I think ours was about 2.5 hours and too long. Getting a guide that is interesting is a big part of that. We couldn't ask questions due to ours being prerecorded.