I think I have now found what I was looking for. The then book was Topo-guide des sentiers de randonnée : GR de pays, Paris à pied published by FFRandonnée (Fédération Française de la Randonnée Pédestre) in 1997.
This site apparently refers to the same two walks (and also shows maps):
A newer guide, Paris ... à pied from 2016, contains descriptions of three walks with the following summaries (translation courtesy of Google Translate). It might be a newer version of the same book with routes no. 2 and 3 being those I was looking for.
Traversée N ° 1 is west-east oriented. It crosses the Seine twice but
is largely left bank. The route travels through picturesque
neighborhoods, such as the Latin Quarter and the Montagne Ste
Geneviève, evoking the Philippe-Auguste enclosure, and the lower
Bièvre. The circuit also allows to take several large green areas:
Champs de Mars, Luxembourg garden, Jardin des Plantes or the park of
Traversée N ° 2 is a North-South route, with more pronounced relief,
which connects two major Haussmann parks: the parks of Buttes-Chaumont
and Montsouris. It allows to survey some historic districts such as
the Marais and its mansions, the medieval streets of the
Maubert-Saint-Séverin sector or the Mouffetard district.
Traversée N ° 3 is oriented West-East, connecting Porte Maillot to the
Porte Dorée, and offers you a discovery of the old villages of the
capital. The Musarde route through Parc Monceau or Belleville,
exploring the Buttes-Chaumont Park, climbing the Montmartre hill and
the Belleville plateau, or along the old Petite Ceinture railway.