They are both on the same day, which for me is a big shame as we like to have our stall at both but it's not practical to do that. So I hope that next year they are separate.
However, the Marple Christmas Cracker officially runs from 10am-3pm but it is expected that most Cracker venues will finish at around 2pm. The Winter Wonderland starts at 1pm, so for people attending the events the overlap is not too bad - you could certainly go to both and it may bring more people out for both events.
Apparently VIP Taxis plan to run a shuttle service between the two venues.
In answer to Susan's question, yes, the Christmas Cracker is the event with stalls on Market Street, Derby Way, Santa's Grotto etc., as last year.