Just to make your writing life even more fun: Canadian laws may differ slightly from those in the U.S. if the courts have decided cases in a way judges here wouldn't.

But, in my experience, authors of historical novels are likely to have more trouble with the heirs of the recently dead rather those of the long-dead. That's especially true if the heirs of the recently dead are executors who see themselves as defenders of the reputation of the dead. Some of those may seize on any chance to sue, such as a copyright infringement.