Just to tie the "navvie" end up: the work cutting the canals was fiendishly hard - up to ten tons of soil being shifted per man each day was not untypical - and could only be done by the huge intake of calories, mostly by eating and drinking hard. I have seen estimates comparing these workers with top athletes and weightlifters today.
The result was that they were generally as pissed as newts on a permanent basis, only sleeping when exhaustion overtook them. As such, they were feared by the communities they came past, but thankfully they were rarely around for long.
Many were Scottish emigrés of the Clearances, and Irish from the famines. As the loads created in the Industrial Revolution increased both in weight and frequency, the roads broke up, in some cases becoming up to half a mile wide as carriers tried to find a way past the mud pits created by previous loads. Zigzagging in search of a way through could massively increase the milage and slow the loads, and so the first work found was in creating the turnpike network of built toll roads. That was soon supplanted by the canal network, as despite the sloth by which one might think the horse hauling a barge portrays, it was both far faster and far more productive: a wagon might be hauled by far more horses and cover a far shorter distance each day, and a canal barge and buttie carries the same as a dozen wagons or more.
However, the creation of the railways made a far more rapid transport system, and killed canal construction: the navvies followed. Although the explanation of them as canal navigators is factually correct, there was also a subtext that many were formerly navy, sailors discharged from the Navy in 1815. When the UK railways were saliently constructed, many emigrated to build the railway networks of the US and British Empire.
Many of those who remained in the UK became the Didekoi, the Irish Travellers despised by the Rom Gypsies. Others became dockers, as they were experienced in handling huge weights, and eased back gradually as cranes took over unloading ships.