Barry:
There are no canvas's that should not be varnished in reality! All microporous inkjet receptor coatings open the paper to all sorts of atmospheric contaminates, so unless you are framing them under glass, their life expectancy is up for grabs. Most people doing canvas prints for hire, print them on water resistant matte canvas, and then apply a vinyl acrylic top coat to seal the surface and protect the print. Glossy canvas's are a "cheap out" way of getting a gloss look without applying a protective coating.