This song is from Vendée.

Notes

"Guillaneu" (guilanneu, guillanée and other guiannée, guillonnée, guillounnée etc.) means "New Year's gift". The word comes from the phrase "Au gui l'an neuf" (lit. "To the mistletoe the new year") itself coming from the Celtic/Gallic phrase "O ghel an heu" (May the wheat germinate), a formula exchanged as New Year's wishes in older times, like the current, "Bonne année !" (Happy New Year!).

Guillaneu is also a mystical horsewoman riding the horse called Mallet that's found in French folklore songs from the 19th century, especially in Vendée and Poitou.
For more information about it, read the very interesting article from Christian Souchon's website, and this one about the horse Mallet and for those who understand French, here's the one about Guillaneu from Wikipedia.

Thanks and Acknowledgements

Source: Anthologie des chants populaires français, tome 3. Joseph Canteloube.