I recently received the "Grand Circle Cruise Line 2013 Worldwide Small Ship and River Cruises" document.
On page 118 there is a photograph that identifies a building as the "Lutheran Cathedral". It looks to me like the Uspenski Cathedral, which is Russian Orthodox. The Lutheran (or Helsinki) Cathedral is several blocks away, and would not appear in this photo.
Anyway, I'll be going there next month with GCT, and am looking forward to seeing Helsinki.