The Canal & River Trust have created free downloadable illustrated maps and activity sheets for 100 waterside walks in England and Wales. There's also a free mobile app which you can get through the Trust's website: http://canalrivertrust.org.uk/places-to-visit.
Driving with Dogs is helping the Canal and River Trust to make their walks more widely known, and these walks are already being added to the DwD site - with extra info for dog walkers (poo bins, basically!).
The walks are printable PDFs, if you prefer these to an App.
Canalside walks are really great at this time of year, with lots of wildlife to spot on the canal banks and many of the waterside pubs are dog-friendly.