In fact, oddly enough, Brittany is the one region that does have this tradition -- they're called pardons and we have several paintings that Paul Gauguin did of various pardons.
In Brittany however rather than being just at Easter, they last from Easter to mid-August (Assumption). In Locronan, they have two "tromenies" in July.
It does seem like most take place in July and August (in hopes of better weather, I am sure!) but I found a reference to a pardon to be held in the town of Livré-sur-Changeon, in the Ille-et-Vilaine département that will be held on Monday April 18 beginning at 2 pm. "Le Pardon de Saint-Nicodème"
They reference the website of
I don't know if that is anywhere near the area you are planning on being.