I'll take a third option and vote for a newly spawned NPR shooting at a survey ship. Maybe one of the Manchurian ships that are behind the newly claimed Russian system.
If this lead to Manchuria blaming Russia, it would basically be the plot to a sci-fi novel :p
As far as conflicts.. the only way I can see the Centauri having a chance is if the Brazilians are idiots and the Centauri min/max the Aurora rules to hell. Assuming that doesn't happen, a landslide victory in space for Brazil, but possible difficulties on the ground since they don't have missiles to nuke any Centauri ground forces. On the other hand, once they control space they can attack the Centauri worlds one by one, so eventually they'll win.
Germany/US vs the Caliphate.. in a fair fight, this might actually be pretty close. But if the US and Germany launch a surprise attack while most of the Caliphate's forces are in Earth orbit, they'll be at a huge disadvantage. Even assuming they launch all their FACs in time, they'll have lost the chance to soften up their foes with long range FAC delivered missile strikes. So my prediction: Caliphate forces get shredded, but take out most or all of US and Germany's heavy units with their meson cannons, leaving both sides severely weakened. Germany will probably be more help on the ground than in space, since neither side is likely to want to bombard the planet and troop numbers are going to count.