Peter:
Gloss optimizer is not a substitute for spraying canvas prints. Using a vinyl acrylic top coat, protects against mild abrasions and water spills, but most of all, seals the microporous receptor coat against atmospheric contaminants such as ozone, which can degrade pigment inks.
I've been using Rosco's Clear Acrylic Gloss transparent Glaze #5580 diluted 1:1 with water, and sprayed using an HVLP spray gun. Been using this product for 15 years with excellent results.