You are spoiled for choice. The northwest shore of the lake is vertical to over 250 feet. Cliffs cover the entire stretch from Blueberry Point (G), just south of the indicated GPS point (E), to the Cathedral (C) and the wreck of the Mayflower (A).
The A, C, E, G remarks are references in Scubarama’s page.
More details available at Scubarama’s Massawippi page:
in French,
English (Google Translate).