I have had used Mpix and Canvas On Demand for a few large canvas prints. Mpix offers a slightly better product IMHO but Canvas on Demand has better pricing. Both services are capable of getting you print in the neighborhood of 24x36. PM me if you end up using Canvas On Demand as I think I have some coupon codes for you to use.
I have had bad luck with Canvas on Demand.
Three tries.
First, bad color balance. Maybe my bad....I wasnt able to softproof.
Second, different image, blown whites, no details despite using their profile, softproofing, leaving headroom for whites. They quickly offered to reprocess, no charge.
Third, reprocessed second with further adjustments on my end to allow even more headroom on the whites. Better, but far from professional. And the canvas sagged out of the box.
Moral: You get what you pay for. Or at least, I did. Not worth it.
I have used canvas on demand 3 times, mostly happy with them. Although a B+W print I had made lost more detail than I would have liked, good pricing though.
Used Canvas on Demand about 7-8 times, always happy with them. There may be others out there that are better, but these are the only guys I've used so far.
We are a very affordable, and reliable canvas printing service, we can print up to 44" at very high quality, the canvas is hand stretched, using 38mm gallery frames, all prints come ready to hang and there are no hidden charges, please check out the site, we aim not to be beaten on price.
I have used several places, and by far my favorite has been The Photo Touch, out of Colorado. They are a bit pricey, especially compared to say Costco, but the quality has been far superior. They also have a nice option of mounted to MDF which makes it very easy to frame in case you don't like the wrap style (which I don't).