The S Note application seems to have a limitation I can't get by. The only workable area is the exact size of the screen. Is it possible to change the size of the canvas?
As far as I know it is (still) not possible. You can now "zoom" the canvas which might suit your purposes. The original physical extents of the canvas remain.
As an alternative, I highly recommend Squid (formerly named "Papyrus". I have looked for apps specifically for an "infinite" canvas and find Squid quite suitable.
My only beef with Squid is that it cannot be configured to replace Samsung's action notes (Samsung's fault; not Squid's). It would be nice to be able to capture notes using Squid without unlocking the phone.