My guess is that HN Protective Spray is rebadged Premier Print Shield, or that both vendors are sourcing their private labeled product from the same manufacturer. Label is different, but the can's design, nozzle performance, viscosity and solvent formulation appear to be identical. You can use them interchangeably without noticing any differences. Also, samples having been coated with both products are in test at Aardenburg Imaging and the general light fastness enhancement to the samples is the same. I personally and routinely use either product with excellent success on Hahnemuhle Photo Rag Pearl, my favorite satin/luster "traditional photo" paper. This paper has it's own distinctive "look" not closely copied by other media, holds the wet spray coating very well without sag, and dries down beautifully with very little change in surface appearance other than the elimination of all differential gloss (which is relatively low on this paper to begin with, but I'm fanatical about removing all traces).
The challenge to working with low viscosity sprays like HN Protective Spray and Premier Print Shield is applying enough to make a substantive coating (two coats optimal) yet not applying too heavily that the low viscosity solution puddles or sags before drying.
While it can work for canvas, it won't necessarily alter the canvas surface patina which many artists actually intend to do when varnishing (ie. use a varnish for decorative gloss/color gamut enhancement as well impart protective barrier properties. It's also undoubtedly a very expensive option compared to the aqueous-based varnishes that most people apply with HVLP spray guns or rollers, so most artist wouldn't use it unless they produce only a few canvas prints each month. The coating resin is acrylic, but not being an aqueous emulsion like ClearStar ClearShield, BC Timeless, etc, it may be more prone to cracking when the canvas is stretched even though the thickness of the coating will be quite low.
The only actual experience I have with HN Protective Spray/Premier Print Shield on a canvas medium is with the Kernewek Fabric "St Ives" (see: http://www.aardenburg-imaging.com/news.67.html
). This is a unique "infused" inkjet medium that retains the weave of the fabric exceptionally well because the inkjet receptor layer is infused into the fabric rather than production top coated like most canvas/inkjet media. The conventional overcoats tend to fill in the weave pattern on the canvas. Spraying with HN Protective Spray alters the delicate structure of the St Ives fabric very little, and it looks essentially as if no coating was ever applied yet provides some barrier protection. One artist colleague I print for on the St Ive's fabric will sometimes desire a thicker decorative coating on the Kernewek fabric. He applies the HN spray as an undercoat on the Kernewek Fabric, then rolls on a top coat of aqueous-based varnish (I seem to recall him saying ClearStar) with very good results. The reason he does this is because testing at AaI&A has shown some chemical compatibility problems with the aqueous chemistry needed to emulsify the resin in the acrylic varnishes and the aqueous pigment based inks (i.e., light fade resistance is impaired rather than enhanced). The HN spray is thus acting as an intermediate barrier coat between the encapsulated ink particles and the aqueous acrylic emulsion chemistry.