There are a few threads on canvi
I've used
http://www.1clickprint.com/ and I was happy with the result, but the reason for picking them was that I needed a custom size as was doing a pano.
WRT noise you might get away with it a bit more on a canvas, just as it's not flat, but to be honest, I'd blow it up and run some noise reduction on it first then send it to be printed..
One thing to consider is that many of the cheaper canvas places use shallow frames, 1click us good quality frames.
Someone else may be able to share their experiences... what size are you looking for out of interest?