The one from central manchester out to the velodrome has some nifty 'cyclists dismount' cobbled ramps at the locks, much fun, worth scally dodging for.
I've seen commuters on London canal paths and they seem to think doing 30kph around blind bends is legit. I don't think there's too many physical obstructions just other riders and the 4-across dog walking teams.
Considered canal path commute but I reckon to avoid the shitheads I'd need to be using it at 5am...