I am a huge fan of alternate history. Real history as well, for that matter. I was kicking around a scenario I haven't seen done before. What if the French had dominated the North American continent?
I would likely start in the present day. The English settlers in Massachusetts would now be a semi-assimilated ethnic group like the Cajuns in Louisiana. They would live under French rule, but have a distinct culture. They would likely have been relegated to the less-desired areas of the Bay State. Paradoxically that would likely mean the Cape and Islands (As these were never good farmland). Known colloquially as the Grims (for Pilgrims), these stern and dour holdouts would likely have a culture as insular as the Amish, clinging to their stern Congregationalist faith. I could see them as sailors, perhaps doing well in the Age of Sail, but now slowly being inundated by a sea of French tourists from the nearby cities of Noveau Lyons (Boston) and Nouveau Rouen (New York). Or perhaps the Dutch are also still players in the area, and Nouveau Rouen is still Niew Amsterdam.
How could the French win? I can think of several causes:
Virginia was a bust: Jamestown wasn't the first attempt to settle in America. The fabled Roanoke colony failed a few years prior. So what if the Jamestown settlers had a bit worse luck? Maybe Pocahontas didn't love John Smith. Powhatan decides to raid in force, wiping the colony out. Or maybe their famine is worse, eventually starving them into extinction. Perhaps the fad of tobacco doesn't catch on, depriving the colony of their one main trade good that they depended on in the early years. A few worse turnings and the fragile colony would evaporate.
King Phillip's War: In our history this conflict with the local native American tribes decimated the early colonists. Fully a third of the settlers were killed, and many settlements were abandoned. It eventually led to the merger of the Massachusetts and Plymouth colonies, and ids why there is no state called Plymouth today (although Plymouth is still an enormous town by Massachusetts' standards.). If the Wampanoags had been a bit more successful, and the colonist been a bit less lucky, they could have been pushed right back to the shoreline. It would have taken decades longer to recover, right up until the mid 1700s, bringing the colony into the French and Indian War era.
The Huguenots are allowed to settle in America: This was truly a missed opportunity for the French. The Huguenots were the French protestants, forced into exile by the crown, but not allowed to come to America. Many settled in England, becoming staunch Englishmen in the process. If the French government had decided to use them as colonists, like the English allowed the Pilgrims to do, they would have remained loyal French citizens, and would have had a greater stake in building a viable colony than the run of trappers and priests did in our history. The French Canadian holdings would have been much stronger, and there would likely have been a much more concerted settling of Maine and Vermont territory by Huguenot settlers.
Bad luck for the English in the French and Indian War: This conflict was arguably the first 'world war', with conflicts springing up all over the globe wherever the French and English were competing. The upshot in our history was that France lost, losing all claim to India and much of America. Their empire never truly recovered. Assuming that the English had not done well as settlers, and the French had, the English crown could have retrenched, and allowed France to take India and America, just as the opposite happened in our history.
Just some random thoughts :)