This is one of the cases where facts are made.
Lets assume the aliens do land somewhere. Then of course the state in which they landed will deal with it. They will probably send their army to secure the landing site, and then send representatives to speak to the aliens once its been established that those aliens are peaceful.
So, whoever gets their hand on them determines what they hear, first.
Of couse this might not sit well with the neighboruing states. If another state has superior military power and thinks he could benefit from it, he could try to invade and seize the opportunity.
Once the dust settles, its politics and diplomacy. The aliens are a precious commodity, everyone will want to talk to them. So there will be deals and treaties signed that govern who gets access and when. rest assured, the country where they landed will want something in return when they let foreigners speak to the aliens.
Thats assuming the aliens stay there. We don't know. They might just take off, find another spot to land on the Earth - rinse and repeat all of the above.
If they +do* tour the world on their own, at some point demand will drop, and it will get harder for each subsequent hosting country to get favorable deals.
The fact of the matter is that it would be solved how all international disputes get solved. Either by force (militaristic) or through politics and diplomacy in the form of deals and treaties. everything else is mere speculation. There is no single government that rules all of Earth, no comitee that could represent the whole planet.