As Yankee_Sailor has pointed out, the figure of 2 million can only relate to the eventual numbers of United States and British Commonwealth troops in Western Europe: his figure of 150,000 in the initial landings is approximately correct. One of the problems of invasion by sea is that it is very difficult to land enough men and their supplies to ward off an immediate counterattack.
I do not know the exact numbers of German troops in France in 1944. It probably depends quite a lot upon how you define them. For instance, the Atlantic Wall was garrisoned by largely low grade soliders, e.g. ones wounded on the Eastern Front, whereas mobile usints would be brought up after the invasion.
However, the real issue in landing allied troops in 1944 did not relate to the numbers of troops but the quality of the defences. The Germans had built massive fortifications in the Calais area including huge concrete gun emplacements at Cap Gris Nez
armed with fifteen inch battleship guns (the British had large guns called Winnie and Pooh near Dover, but they were not nearly as well fortified). No country could have afforded to continue such fortifications all round the French coast e.g. to Normandy. In addition, the land between Calais and Dunkerque is marsh (it is dyked like Holland), and that further West from Calais to Boulogne and beyond has chalk cliff on the coast. Not good for invasion purposes. In addition to the strength of the defences, Calais is sufficiently nearer Germany than Normandy, with consequent implications for the speed with which Germany could bring up reinforcements to oppose the landings.
Not least, the Germans expected the landings to be near Calais. The value of surprise in warfare is not to be underestimated. The Allies took huge efforts to maintain surprise. For instance, the invasion was planned from Dover Castle, in the front line opposite Calais (within shelling distance of those guns at Cap Gris Nez). Who would choose such a crazy location if they were not going to invade across the Straits of Dover?