There are several harbours in which your can tie up. La Grave at Amherst (Havre Aubert), Grindstone Harbour (Cap-aux-Meules), Etang-du Nord harbour, Grand Entry Harbour (Grande-Entree). Grosse Ile and Entry Island harbours are English speaking communities. There are restaurants near all of the harbours, except perhaps Grosse Ile.
I don't know if any of the harbours having showers but there should be toilets on each of them. The tourist guide should say....
Old Harry Beach has a beach house with paid showers and toilets. But Old Harry is on the northern most inhabited island relatively close to Grand Entry Harbour.
There are seven inhabited islands and twelve islands all together. Will you have a means of island travel?
The travel guide http://www.tourismeilesdelamadeleine...g-696-home.cfm