Cann Lake was the name given to one option to tackle the problem of what could be done if the full A556(M) was ever built. A new road had been proposed in various guises to serve M6 J19, and most of these options required Knutsford services to be demolished.
In the event, the A556(M) was postponed indefinitely and Lymm truckstop was expanded instead. Although the new road opened in 2017, improving M6 J19 was delegated to another scheme.
The unbuilt plans were first identified in a planning document, which refers to new services being planned at "Caan Lake". That location doesn't match up with anywhere on the map, but this one is near a street called Cann Lane, which could be what it should have been called.