I know Glowforge isnt shipping internationally yet but some Canadians have their machines ready. For those that don’t know where they are going to get materials I would take a good look at engraving-supplies.ca. They off a ton of awesome materials.
An account is required but a quick look shows they are cheaper than proofgrade stuff for lots of things. (23.5"x11.75" - 1/8 walnut ply for $15 cad). They also do $15 flat rate shipping and free shipping above $300.
They also have a bunch of local locations (any trotec show room pretty much) in case you want to pick up.
Edit: I don’t know if their stock size will fit in a glowforge but I don’t have an issue running it through a table saw to get it to the needed dimensions personally.