One of the benefits of using the browser is that the generated PDF will be using vectors/fonts etc whereas Canvas will be mostly an image in the PDF. Not a big deal for the most use cases.
I feel like it’s probably not a leap to go from this to having a PDF renderer as a backend. The trickiness is in the layout, which this is already doing. Looks to be a lower level api and a way to render to absolutely positioned html. That gets you most of the way there.