Boucherie de Paris in Côte-des-Neiges has excellent slab bacon. Very meaty, nicely smoked (maple wood, I believe) and made by a small local firm. They'll slice it to order, either with their slicer or a knife.
Boucherie de Paris
5216 Gatineau between Swail and Jean-Brillant (metro CDN)
There's a charcuterie on St-Laurent near Marie-Anne called Charcuterie Le Traiteur Du Terroir that had a really smoky bacon you could buy in a chunk or get them to cut for you, so they would probably be flexible on the thickness.
My husband says he thinks this charcuterie is gone from the last time we walked by... I'd be really sad if so, so does anyone know if it's still there?