IMO the idea here is of a blank canvas. They supply & suggest the woods, hardware, inlay, electronics, etc, but these are just the tools you choose to customise your instrument to make it into something unique and high-end.

Canvas can be used to mean paintings as a collective noun.

So in this use, the set of Custom Deluxe Models are like a set of paintings. The set of models are paintings/portrayls/representations of the type of artistic work that goes into each Custom Deluxe instrument.

Each Model is an individual/custom creation, like an individual/custom painting.

The author of the text is using "canvas" in this somewhat unsual way to heighten the idea that each custom instrument is a work of art made just for you - made uniquely for each customer.

REFERENCE:
"Canvas: paintings collectively; ...; also used figuratively to mean ‘a wide range, a large expanse.’
Example: canvas of fancy, 1822.
Dictionary of Collective Nouns and Group Terms. Copyright 2008 The Gale Group, Inc. All rights reserved."
http://www.thefreedictionary.com/canvas

The Custom Delux models ***underlie/serve as models for/are at the basis of*** beautiful high-end instruments that have always been the benchmark of our shop.