Flaw to using non-www domain a canonical?
I love the idea of short, clean urls like example.com over www.example.com, and certainly whichever one is used should redirect to the other. However, as I have researched the matter over time, I've come to the conclusion that using the non-www url as the canonical url is a liability if it ever comes time to host static content on a separate domain without increasing the transfer size with cookies.
Non-www domain shares it's cookies with all subdomains
In other words, if http://example.com is your canonical url, then it will very likely include cookies. Due to the way that cookies get set, those cookies will be shared with all subdomains, like users.example.com, dev.example.com, www.example.com, and most importantly, images.example.com or files.example.com.
Thus, if you want to serve static file content from a separate subdomain, you'll end up bundling cookies from the main site with them, and increasing the transfer size of the http request.
In which case to prevent passing cookies with the static content, you'd need to buy a completely separate url (e.g. examplefiles.com).
www domain keeps it's cookies compartmentalized
Conversely, if you set www.example.com as the canonical url, I believe the cookie only applies to that www. site, and not to any other subdomains. In that case, you save yourself the need to buy and maintain a second url to avoid serving cookies with your static content, you just make sure that files.example.com or images.example.com or the like is configured to -not- serve cookies.
Any mitigating factors?
Is this analysis correct? Doesn't this problem make use of a short, non-www url as your canonical url slightly non-future-proof, in this small, but potentially important-down-the-line way? Are there other mitigating factors that I am missing, like a method to ensure that the cookie is only set for the canonical non-www short url?