Looking at the world cup draw, it's highly likely to be Argentina*.
Sigh.
*Ireland are in Pool D, with Scotland, Uruguay, Portugal. Winner of D plays best 3rd place of B (one of Georgia, Romania or Italy), E (Samoa or Japan) or F (Wales or Tonga).
The winner of that match plays the winner of D (it's going to be Argentina out of pool with Fiji, Spain and Canada) who'll play 3rd from A (Chile or Hong Kong), E and F.
Not sure how the allocation of the 3rd place is going to work, but either way, it's almost certain to be Ireland V Argentina barring a massive upset.