I suspose its possible to reach Poland, but it still wnt be a cakewalk. First the Allied logistics support has to catch up. Then the German defense must be beaten down. Even before assualting the Rhine an extensive preparatory campaign would have to be done. Mostly air & long range artillery isolating the Rhine defenses then softening them. Even if the Germans abandon France & Belgium in June it would be September before the Allied supplies are suffcient to start artillery preperation, and the for the air bases were ready for the fighters & medium bombers. By the time prepartory attacks are accomplished it would be October or November.

Then there is a much stronger German military facing the attacker, not the wreck of march 1945. Even with a massive air attack and realatively fresh Allied infantry it will a slow stiff fight. The big advantage of course is the faster collapse of German industry supply to the ground & airforces. Historically this took effect in Febuary of 1945. If the Allies close to the Rhine valley in Sept 1944 this supply transportation collapse could begain in December or even November.