Canvas in the luxury bag context typically refers to a coated or treated fabric — a woven textile base with a PVC or polyurethane coating applied for waterproofing and durability. It's not 'natural' canvas in the traditional sense but a highly engineered material that outperforms most leathers for everyday use.
Louis Vuitton's Monogram and Damier canvas, Goyard's Goyardine, and Burberry's coated cotton are all luxury canvas products. The defining characteristic is that the material holds its shape and surface regardless of weather or rough use — a significant practical advantage over untreated leather, with virtually no maintenance required.