We did it in 4 days/5 Nights - and found we were pushing it in places. (OK so the weather was dreadful)
We did nights in
Whitehaven
Keswick
Langwarthby
Allenheads
Sunderland
I would definatly get the Sustrans map, but do some careful reading as there are several hills that can be avoided by going on 'main' roads - for an urban cyclist the main roads are not main at all.
If I was to do it again the one change I would make would be to avoid some of the sustrans traffic free variations and take the logical (if busier) route.