Think this will work as a canvas top dressing?

[Perfectlap]

no it won't work. In order to keep a canvas top looking new you have to be able to clean it with the correct cleansing agent. Otherwise dirt gets into the fibers and each time you stretch the canvas from opening and lowering the top you end up with wear marks, eventually that rips, just like a pair of jeans. The Raggtopp cleanser is not meant to be a permanent sealant for precisely this reason, to allow for easy cleaning of the top, down to the fiber.
Unfortunately each time you get a bird bomb, road grit and grime on the top you have to rinse and repeat the whole process. But that's how it goes with canvas. If you want to be skip the hassle of cleaning fabric then a vinyl top would have been the way to go but those end up looking a little generic and cheap after a few seasons in the summer and some of those spots/stains just never come out of vinyl. Think of the top as a tuxedo for your Porsche.