Déjà vu is a French word that literally means "already seen." People who experience Déjà vu usually get a momentarily weird feeling of being familiar with something that they ought not to be familiar with. Indeed, they ought not to be familiar with that thing because it is actually their first time being in the location, situation or event.
The feeling is not different from Maurice's case because he is visiting a foreign city for the first time but somehow momentarily experience a weird feeling of being familiar with the city's landscapes which is actually foreign to him.
To "insure" is typically used in a sense to protect someone in some way or to set in place a policy that will do so. I would go with to make certain. The other options do not make that much sense, as domestic tranquility is a very good and necessary thing.
