Hi Jude:
Basically what you're planning to do simply isn't possible. The canvas prints you see offered (usually at horrendous prices) by High Street photo-processing shops are true photographic prints. They use a canvas which has been specially coated with the same sort of silver-based chemical that is used in the manufacture of the photographic paper that is used for making prints from negatives. That canvas is then used in exactly the same way that the photographic paper would be. (i.e. it's used in a darkroom, where a negative is projected onto the canvas and then processed with a succession of chemical solutions).
So, unless you've got access to a darkroom, an enlarger and all of the specialist chemicals, you can't make canvas prints with the canvasses from Dunelm Mill.
However all is not lost. There is a way of getting canvas prints from an inkjet printer. Please see my post here:
http://www.theanswerbank.co.uk/Arts-and-Litera ture/Question697229.html
Chris