Must be a local term in Hull. I've never heard of this expression in Montreal or elsewhere in Quebec. I couldn't open Les Petites Annonces section in Le Devoir, but La Presse certainly doesn't use "garconnerie" to indicate a bachelor. Normal terms used are:
studio
une chambre
deux chambres
trois chambres
penthouse
chalet
condo
maison
etc.
Garconnerie often implies a place of sexual nature, usually a place for boys, "garcons", to go crazy for, hence garconnerie.