Printing matte canvas with photo black generally gives low contrast, mushy dark areas when compared to the same image printed with matte black. To my eye, photo black on canvas is simply not acceptable from a visual standpoint. Also, photo black ink on canvas tends to smear if you roll on coatings.
Of course the 7600 requires a cartridge change to go from matte to photo black, so it's a tough call for someone who also needs to print glossy papers. There are some "glossy" canvases such as BC Crystalline that are best printed with photo black ink, so there's an option.
The manufacturers claim that some of the glossy canvases kinda-sorta do not need to be coated. But although they are fairly rugged uncoated, IMHO they absolutely do need coating, both for tonality and resilience. The catch, glossy canvases can only be sprayed, not rolled. Another catch, glossy canvases are generally more expensive than matte canvases.