I had a bimini top on my CJ5 Jeep. Window frame to roll bar, no frame like on a boat. So I believe a Bimini means a top that offers protection from sun and rain.
However, I believe when you inquire to purchase a bimini for a boat it normally means the canvas and frame. Most are custom built so an on-line store will probably not sell just the canvas. There are too many variables as to bends, mounting places, number of bows, bends in the bows, etc.
Sure you can buy a cheap basic bimini on Amazon or such places that are based on a certain width, height and mounting option but they will not include cutouts for aft stays, arches, etc.
Plus sunbrella does stretch over time. Enough that all my readings says that a quality canvas maker will not use the old canvas as a pattern for a new bimini. He'll want to measure and create a template. When I started sewing canvas for my boat a long time friend and auto upholsterer by trade warned me to never use old upholstery as a pattern. He said to copy from it but always use a new template and measurements. Old upholstery and canvas stretches too much to get new nice and taught.