What's the best way to create a "portrait smooth" canvas surface with less tooth than the average canvas - and less absorbency? More gesso and light sanding, or would trowelling on gesso, or maybe one of the GAC products acting as a barrier, is the way to go?
While our normal gesso is fairly sandable, it often takes some time to become dried enough to do so
without a lot of gumming up of the sandpaper. Even with that, the acrylic resins are thermoplastic, meaning that as they become warm, they also become softer and of course tackier. If you do sand it, take care not to generate too much heat.

The GOLDEN Sandable Hard Gesso is a much better choice for achieving the smooth surface, however it's designed for panels or stretched canvas on panels because of it's propensity to crack if overly flexed. We've been working with woodworkers and they will tell you the key to achieving smooth sanding is to use grits from coarse to fine, but do not change grits more than 20 at a time, meaning go from 220 to 240, and 240 to 260. This results in very smooth surfaces with no "swirling".

I would think that once you achieve a smooth gesso surface, the Acrylic Glazing Liquid would be a good product to seal the surface with before using color.