I am wary of canal towpaths or the waterways themselves. In a boat of some type, you would be terribly exposed and with no easy escape from an aggressor close by on the bank. The rate of movement would be low also. Added to that is the likelihood of the waterway being easily blocked at any point and the overhead bridges etc. You would be a sitting duck.
Being on the towpath is not much better. You are bounded on one side by the canal itself and would have few options of manoeuvre if a possible threat approached. Moving on bikes would compound the problem of hazard identification in a useable timeframe.
I am not ruling out canal routes altogether but I would be very wary of using them. They also tend to move from one urban area to another and "A" roads often follow similar land contours which means the likelihood of meeting strangers can be higher where the two transport routes are close together.
I think that quite a few non preppers may also opt in to the canal network route idea and that does not include the boat people or the nearby residents themselves.
Footpaths, green lanes, bridleways and farm tracks across rural areas would be my choice, preferably at night and with night or thermal vision if ability and finances allowed. This is of course if ruling out the vehicle option. A waterborne vehicle on canals would be too slow for a bug out option. More a slow gentler progress but with increased risk. IMO. Large rivers would be a different scenario and wholly possible. Location, location, location as they say