I think the question to the original question would have to be “to what end?”
The Whitley and Wellington were both firmly medium bombers, with maximum bomb loads of 7000lb and 4500lb respectively. The Manchester was always intended to be a heavy, with a bombload over 10,000lb. On checking, the MTOW for the Whitley was around 33,000lb – HALF that of a Lancaster!

Also the Manchester was more aerodynamically refined, and a pioneering airframe in modular construction – the same basic design was stretched into the Lancaster and later the Lincoln by such simple measures as increasing the spacing of the ribs in the wings, adding wingtip extensions etc.

Really, what it boils down to is that the Whitley and Wellington were first generation monoplane bombers, whereas the Manchester was second generation.