Artillery and aircraft shall bomb Romanian logistics in Transylvania, and across the Danube. This should make it easier to capture enemy troops. First we'd advance using tanks and infantry from the north and south (purple), attempting to hug the Danube in the south and make a general breakthrough in the north. Then we'd try to reach the mountains in the north and south (Blue), us now pinning down a force in the center. Then with enemy logistics only allowing escape through the mountains (Green), we'd attempt to destroy the remaining troops due to our mountain logistic bombings. The southern pincer's flanks will be covered by our northern attack, as in order to attack the southern pincer, you would need to draw forces away from the north, weakening that front and allowing us to launch an attack from there.
This is Phase One, if Romania doesn't accept peace (which is Bessarabia) after this, then we will initiate Phase Two.