Part of the reason the for-canvas coatings are so expensive is that they as designed to be flexible enough so you can stretch the canvas (within a reasonable period after coating).
Glamour II represents pretty good value because it is rather concentrated. 1 gallon over GII translates to about 1.2 to 1.5 gallons of coating that you can supposedly use "straight from the can" such as Clearshield and the Lexjet product. Of course handling the thicker-than-molasses GII concentrate up to the dilution step can be a PITA by any measure, until you get your technique together.
Yes you can get different finishes just by the way you apply the coating. But I think for maximum protection and durability and minimum sub-surface scattering you should always apply very thick, wet coats and only vary the mixture of matte and gloss to get the desired finish. As little as 1:9 Matte:Gloss gives you a distinctly less-than-glossy finish, at about 50:50 you are very distinctly matte. It takes about 6 hours for GII to dry to the point where you can judge the finish, which gradually loses it's gloss for long after it is dry to the touch.
You must coat canvases unless you plan to frame them under glass or plex. Uncoated matte canvas prints can look quite nice, but in a way that can't be duplicated by a matte-coated canvas. Coating just adds a different dynamic, no matter what you do.
Coating pulls down the blacks quite a bit and increases the overall apparent snap of the print. Basically, just print with your shadows a little more open than you want. I have semi-successfully used special profiles made from coated canvas, but without yakking a lot I would advise you to use profiles made from uncoated canvas, and print up.
Set aside a few weeks to learn the ins and outs of using canvas. There are lots of ins, and many outs. But let me save you at least 2 months...wet coatings, not dry ones. And HVLP is good, but rolling can be mastered by those with high pain thresholds.
And I know certain people who use just regular Home Depot acrylic coatings on their canvases. But I won't tell you who they are, or what they use because I think it unwise.