There's only one
usage of "eh" that is uniquely Canadian. There are several different usages of "eh" around.
According to my Canadian Oxford Dictionary (first ed.):
eh /ei/, interj. informal 1. Inviting assent
(nice day, eh?), 2. Cdn. Ascertaining the comprehension, continued interest, agreement, etc. of the person or persons addressed
(it's way out in the suburbs, eh, so I can't get there by bike).
This is the only usage of eh that can be categorized as peculiarly Canadian, all other uses being common amongst speakers in other Commonwealth countries and to a lesser extent in the United States . 3. Expressing inquiry or surprise. 4. Asking for something to be repeated or explained.
** bolded emphasis mine, from "This is" ... "United States." :)
So, I stand by the classification of the second sense of "eh" as the Great Canadian Shibboleth.
I'm also pretty sure that "beauty!" as in interjection -- which was the *real* subject of this post -- is natively Canadian, although I think it's drifted a bit, probably because of Bob and Doug. :)