I would assume it's aligned to keep collectors from both countries happy... For British collectors, used to medal rotation, Britannia would be right way up. For French collectors, used to coin rotation, Marianne. So the answer to your question is "both"!

The theme of the coin does make a nice change... the 100th anniversary of a peace treaty between two countries which had been at war on-and-off for centuries. Maybe there's hope for the Humans of Earth after all...

Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis