I think the above advice is best really. If you are looking to start selling canvas prints or wall art in general then perhaps it would be best to use a reputable company that already has the printer. Printers are very very expensive and you would have to fork out for materials etc.
When printing canvases, you need to have a) the printer,

the rolls of canvas, c) the inks, d) the frames and all framing supplies, not to mention packaging materials, stretching materials, compressors etc etc etc.
Try someone like
Four Blank Walls for canvas prints. They do wholesale prints from about £5.00 and are probably one of the best known out there for resellers.