Katherine Barber, maven of Canadian English, dies at 61 - The Washington Post - Dictionary

It is an interjection “inviting assent,” “expressing inquiry or surprise,” “asking for something to be repeated or explained” or “ascertaining the comprehension, continued interest, agreement, etc., of the person or persons addressed.” The last listing is “the only usage of eh that can be categorized as peculiarly Canadian,” according to the definition, “all other uses being common amongst speakers in other Commonwealth countries and to a lesser extent in the United States.”