Alan,
you have to take out a one year Bomber Crewm Membership. When Dad and I went we were also given a flight in the Beech 18 as well but not sure if they still do this or not. It is worth every penny and you have a choice offlying over the Niagara falls or the city of Toronto past the CN tower and along the shore.

Bomber Crew Membership – for $2,500.00 you may have the privilege of a one hour flight in the Lancaster (includes donation receipt for $1250*)./

See here:
http://www.warplane.com/pages/membership.html