Might be from Scots-Irish origin like the article suggested. When I visited New Foundland last year, I found a lot of people there has a distinct accent sounding similar to an alternate but similar version of an Irish accent that I don't hear often from the rest of the country. And I do recall hearing quite a few "eh's" during my conversation with the locals of New Foundland.

Also, we don't get "eh" much here in the westernmost province. Might be more of a Eastern Canada or even just a maritime provinces + New Foundland thing.