Restless Are the Sails — Evelyn Eaton

When Paul de Morpain, a prisoner-of-war in New England, hears of a plan to send an expedition against the French fortress at Louisbourg, he decides he will do whatever he can to warn the governor. It is 1744 - a dangerous time to attempt a 500-mile journey by sea and on forest trails.
Morpain brings San, his new Mi'kmaq bride, to the fortress just before the siege. Taking great risks to try to save the fortress, Morpain falls in love with the governor's daughter and makes no attempt to honour his marriage to San. Amidst the turmoil, he ends up on a pirate ship and must face both the tragedy of the events and his own misdeeds.