Towards the end of the 17th century, the Massachusetts Bay colony went through a curious period of expansion. In 1677 the heirs of Ferdinando Gorges, founder of the colony of Maine, sold out the last of their claims to that colony, which came under Massachusetts' control. In 1690, after the outbreak of war with France, a fleet of 14 ships under Sir William Phips of Boston took Port Royal, capital of the French colony of Acadia (the modern-day Nova Scotia and New Brunswick), and Massachusetts gained control of it as well. Finally, in 1691, Massachusetts absorbed the smaller, older colony of Plymouth to its south.
Massachusetts' days of glory were short-lived, however. By the terms of the Treaty of Ryswick, which ended the War of the Grand Alliance in 1697, all territorial conquests were nullified, and the government of Massachusetts was forced to hand Acadia back to the French.
But what if they hadn't? After all, it hadn't been the Royal Navy that had taken Port Royal, it had been the men of Massachusetts. If the men of Massachusetts had refused to hand the city back to the French, there was nothing that the governments in either London or Paris could do about it.
This is the POD. When word reaches the colony that they are expected to hand Port Royal back to the French, they refuse. To all those who demand that they accede to the terms of the treaty, Acting Governor William Stoughton replies, "We took it, it's ours, and we're not giving it back."
The reaction in London is mild. King William III is secretly pleased to have something to show for eight years of war, and to have inflicted a wound, however small, on his old enemy Louis XIV. He isn't afraid that the French will start another war over Acadia (or Nova Scotia as the English call it). Besides, everyone in Europe knew that Louis was trying to make his grandson Philip the heir to the Spanish throne, and as soon as His Catholic Majesty Carlos II died there would be another war anyway.
The reaction in Paris is less mild. Louis is miffed that that heretic William of Orange has gone back on his word, but the time is not yet right to strike back. After Philip is firmly on the Spanish throne, there will be plenty of time to pay back perfidious William and his perfidious subjects.
The reaction in Quebec is less mild still. The elderly Louis de Baude, comte de Frontenac et du Palluau and Governor General of New France, is outraged. If the English heretics think they can get away with this sort of affront, they've got another think coming. Le comte draws up plans for an expedition to retake Port Royal from the "Bostonnais", sends out word to his Indian allies, and gathers a fleet. Unfortunately, the stress proves too much for the governor, and he dies in November 1698, his preparations still incomplete. The expedition is put on hold while the late governor's subordinates send to Paris for a replacement.
The reaction in Port Royal itself is least mild of all. For eight years they've been suffering under the rule of the harsh Puritans of Massachusetts, and now the Puritans refuse to leave as they have been ordered to do. Grim frowns turn into angry mutters, mutters into shouts, and shouts into riot. However, the heretics control the fort that dominates the town, and their ships lie at anchor close at hand, and the riot is quickly put down. By ones and twos, and in small family groups, the Acadians leave Port Royal for the refuge of Quebec, and their places are taken by fresh settlers from Massachusetts and England. Acadia -- or rather, Nova Scotia -- will remain English.
For the time being, at any rate.
(Proceed to part 2 - Brothers in Arms)