Sincere question for the client............why in the world?
So it looks like a real piece of art, instead of a mere photograph.
I use canvas for the same reason painters use canvas. I can thereby create very large pieces that are light enough to be manageable both physically and economically. And I frame them in traditional frames because that's the easiest way to present them, given my resources. But I draw the line at texturing. One has to ask the question...are we doing big photos by expedient means, or are we trying to simulate painting?
I like to create imagery. I prefer to let the physical qualities of the image be those of the media, optimally exploited. Things like texturing are needless affectations, not that different say from black sectional frames and 8 ply mattes, which were at one time themselves a means of avoiding affectation. Say what?
Anyway,
Z-Gel is one way to commit the crime, at around $80 per gallon. Really thick out of the can and your canvas will look like a relief map of the Himalayas in not time at all. But when the Art Trials begin, I never heard of you.
Putting aesthetics aside, from a strictly marketing point of view I don't think texturing is worth it if yer out there trying to schlep art. It may have a small audience at the kind of venues where Novelty trumps Art, but it may also put off more sophisticated buyers with actual money in their pockets.
And regaining aesthetics, it's interesting how many oil paintings show no canvas texture at all and very little paint texture AKA impasto.
Oh, BTW, if you want to texture canvas coming out of an 8300, be sure to put down about two thin coats of acrylic first. I actually tried some of the Z-Gel stuff on giclee prints of my wife's paintings. Let's just say it's a very effective solvent on bare ink. Proved impractical to do at any scale.