Although the use of eh is regarded by some as characteristically Canadian, most usages of eh are spread throughout the English-speaking world, in the meaning of "Huh?" or "What?" or "Repeat that, please".
It is an invariant question tag, unlike the "is it?" and "have you?" tags that have, with the insertion of not, different construction in positive and negative questions.
According to the Canadian Oxford Dictionary the only usage of eh that is peculiar to Canada is for "ascertaining the comprehension, continued interest, agreement, etc., of the person or persons addressed" as in, "It's four kilometres away, eh, so I have to go by bike."
In that case, eh is used to confirm the attention of the listener and to invite a supportive noise such as "Mm" or "Oh" or "Okay". It essentially is an interjection meaning, "I'm checking to see you're listening so I can continue."
Depending on the speaker's tone or the dialectal standard, eh can also be perceived as rude or impolite, as "Repeat that!", and not a request.
However, in Australian and New Zealand English, 'eh' is also found, though as an exclamation, rather than part of a question. He's all right, eh! This has its origins in Scotland, where is can also be heard. The equivalent in South African English is hey, of Afrikaans and Dutch origin.