There are some Javascript PDF viewers. I don't know much about them,
but I just encountered one.
Western Digital uses it on their site. I was just shopping for
drives.... Here's an example. It is slow as molasses on my old AMD64
Linux box with Firefox 20.
Here's an example. (Note you may not get it if you have Acrobat installed...)
http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-800002.pdf
I'd bet it uses the canvas.
Of course, this is not what you want to do. PDF authors usually want
things just as they have written them, and they expect users to scroll
around or zoom to see everything if it doesn't fit. As I understand
it, you want the text to flow to fill what is available at the selected
font size.
But the two problems have some similar requirements. Your requirement
is harder, though, because you need automatic page layout. That's a
tough problem they've been working on for 30 years or more. Some day
they will figure it out.
Kindle is getting better at it. It is not there yet. The readable
Kindle books have been hinted with markup by humans to indicate where
page breaks may or may not occur, etc. Are you willing to do that with
your material?
The self-published books where the author did not have the time or
could not afford the effort can be very hard to read.
Kindle can flow PDF documents. Kinda. In an ugly way. I downloaded a
cookbook on hydrocolloids done like that. It's hard to follow. I can
never tell which recipe goes with which picture. The page numbers make
no sense, you can't correlate them with paper books.
(Even so, I get all my tech books on the Kindle app on my iPad.)