Captain Bender, with his research, is certainly the best person to ask. I know that he was saying before that there were nine Canadian wrecks, and that up to 1,200 lives had been lost. These are just Canadian wrecks. I couldn't necessarily comment on the broader issue on the ocean.
One thing that's unique to military wrecks is that the latitudinal and longitudinal positions of the vessels have been recorded. Even something as accessible as Wikipedia has a list of U-boats, Canadian merchant navy ships, and Royal Canadian naval vessels that have sunk in Canadian waters, with their latitude and longitude and the dates they sank. There is a lot of publicly available information.
I don't know if Captain Bender wants to add anything about the number of wrecks that may exist.