You didn't really state what the problem with the canvas is, is it rotted or ripped? I've seen a couple posts over the years where folks had new ones made but you'll have to search for them. Keystone is still in business so you may get lucky if you call and ask about replacement bunk doors and or canvas.
I've also seen a few posts from folks rebuilding the bunk doors if you want to search. Pictures would help as we can't tell how your bunks are put together or what the damaged areas look like.
I'd think it may be cost prohibitive to hire someone to do the job. However it would certainly help to have an experienced repair person look it over and let you know what your getting into. Might even be able to tow it to a local RV dealer and have them take a look.