A full canvas lining lasts longer and provides a sharp refined look that defines the figure. Back in the day, all suits were made of canvas. It was generally horsehair canvas, which is sewn between the lining and the cloth of the jacket. The canvas allows the suit cloth to drape naturally over you and will mould to your body over time (for the perfect fit). It benefits in the durability of the suit and giving you flexibility in movement (shoulders, elbows), it allows the suit to “breathe” and you don’t need to dry clean it as often.
As the demand for suits increased, a fused suit was developed to appeal to the mass market. Instead of the animal hair canvas a fusible interlining is attached that is heat pressed (glued) to the wool of the suit. While it allowed for suits to be produced at a better price point, the suit may look stiff and unnatural on you. The glue will also wear out over time, and ugly “bubbles” may appear I (this is caused when the wool separates from the fusing). It is also less durable over time and loses flexibility. Fusing is good if you want a price point suit and don’t plan on wearing it every day.
A half-canvas aims to be a compromise between the best of both worlds. A half canvased suit uses a sewn in canvas piece in the chest and the lapel of the jacket, and is fused on the bottom part of the jacket. Having the key areas of your jacket canvassed will still allow for a more attractive, natural drape, will assist with the durability of your suit but still keeps the costs down due to having less handwork.