Volunteers are not as readily available as is sometimes suggested. All charities and voluntary organisations have had to face this. A significant driver has been social change in the second part of the 20C. Immediately post-war, many women were displaced back out of the workplace that they had willingly filled in times of necessity and then looked to fill their time. This was perhaps the golden age for volunteering but by the 70s, with the growth of two income households, the number of people of a physically fit age who are available to volunteer has markedly reduced.
A similar challenge faces the military - 70 years ago many front line infantry could be adequately, perhaps fully, trained in a very short time as they were little more than cannon fodder. Nowadays, much of warfare involved very sophisticated equipment and operating procedures and skills that take time to acquire. As a result the role of the Reserve Army has had to be re-thought as well as the expectations on volunteers. (actually, reservists are usually paid, just not full time)
It might be worth studying that experience to see if it could be applied to canal maintenance and operation. I suspect there are a good number of people who would join and undertake extensive training for that role rather than unpaid, untrained and unskilled volunteering. (I am not criticising existing volunteers, LTRU, but the suggestions for replacing much of the paid work force by unpaid people)