Reminds of a Canadian movie during the war (don’t recall name). The story is of a U-boat landing in Hudson Bay and how the crew is chased across Canada, ending up near Calgary. Banff was also in there I think.
Truth stranger than fiction.
From Wiki:
“It is rumored that in 1944 the crew of German submarine had beached it at the falls when they decided to withdraw from World War II. The rumour inspired a novel written in the 1990’s, but was thought to be unsupported. In 2010, divers searching for three men who died after being carried over Muskrat Falls found a 30-metre long object on the bottom of the Churchill River, believed by diver Brian Corbin to be the missing U-boat [1].”
You weren’t thinking of “The MacKenzie Break” by any chance? It’s the first thing I thought of. Kinda far fetched. U-boats wouldn’t have had a lot of space for freed POW’s.
http://www.imdb.com/title/tt0066064/