In June 1939 how feasible would it be for the Allies to give military aid to the Polish government in Lwiw, and for there to be Allied troops to be sent to the Lwiw salient? Also how likely would a German invasion of Denmark, Norway or the Netherlands be?
If they want to help Lwiw Salient, they need Romania, no questions.
Now, Romania was one of the most Francophile nations in Eastern Europe before the Munich Agreement destroyed Romanian faith in Western ability to protect their allies.
Also Carol II hated the fascist Iron Guard and had their leader, Codreneau, who was assisted by Nazis to take power in Romania, killed, a fact that caused a deep rift with Germans at time (late 1938).
Prime Minister Armand Callinescu was also a strong pro-Allied politician.
IOTL Romania swung to Axis only after the Ribbentrop-Molotov Pact and the fall of France put Germany in charge in Continental Europe. And Berlin was pushing strongly to have free supply from Romanian oil fields, with or without Bucharest agreement.
The Germans assisted and instructed Iron Guard to assassinate Callinescu, then punished Romania with the Second Vienna Award for its past hostility and forced Carol II to abdicate, installing Iron Guard new leader Horia Sima as Co-Dictator with General Antonescu.
But in this TL Romania stayed as pro-Allied nation. Carol II's order to kill Codreneau could be involve even Sima himself, then decapitating definitely Iron Guard and breaking irremediably relations with Germany. Bucharest could allow Allied troops or supply to arrive to Lwiw Salient. At the end the Third Reich will launch likely an invasion of Romanian territory not only for their help to Polish and Allies, but especially to conquest vital oil fields in Ploiesti.
A such invasion, after the attack against Czechoslovakia, could be enough to call the Little Entente and bring Yugoslavia in war.
There was a French plan to land troops in Yugoslavia if Belgrade would enter in war, in order to defend French allies in Eastern Europe, to open a second front against Germany and to entangling it in the Balkans. This could happens.
Before or later, when Soviets will push in Poland and Lithuania probably, Germany will find itself in a bad situation: a war on two front. They can't move troops from East as Soviet Unionis a great threat and Balkan Front open but they can't neither afford a two-front war. At the same time British moves in North are a clear menace to iron and steel supplies from Sweden to German arms industry.
At the end German strategists always teach to push strongly on one front, hoping to close it before concentrate all forces on the other, and, as losing the Rhine Bacine would be a fatal blow for Germany, I can see only a strong attack on Western Front, even if this would mean leave Soviets part of Poland, probably with the double target to expel French from Germany (a first counter-attack in Saarland, to protect Ruhr and act as distraction) and capture Paris (the main attack, probably in the Bulge Region as IOTL). If that will be successful will depend by field variables.
With two or maybe three fronts open Berlin will be too spreaded to execute Operation Wesenburg, at least at the same time as OTL, so I think Churchill's plan to block Norwegian ports to break Swedish-German steel trade will happen, maybe together others Soviet disruptive moves in the Baltic. Germany could occupy Denmark without problems, in order to protect their northern side, and assuring a direct channel with Sweden, but with the Royal Fleet deployed invasion of Norway will be pretty impossible.