After Germany's attack into Poland, FDR and some of the USA leadership could see where global war may be on the horizon and the USA needed to build up it's military strength. Japan's conquest and expansions in Eastern Asia also underscored this urgent need. Hence some of the first efforts at "Lend-Lease" as FDR sought to transform the USA into the "Arsenal of Democracy" against Axis Fascism/Tyranny.
By May-June of 1940 with the fall of France the need gained greater urgency and the UK/Britain was a main focus of USA military equipment and supply production to future Allies. Germany's June 1941 attack~invasion upon Russia soon brought the Soviet Union also into the sphere of American(USA) industrial productions of food, weapons, and equipment to aid in resistance to Axis aggressions.
Shortly after Japan's attack on Pearl Harbor in Dec. 1941 and the USA now at war with Japan, Germany, and Italy; FDR and General Marshall, along with many of the USA Joint Staff were eager to attack Germany ASAP, with plans for a hasty landing in France, likely on it's Western coast. Fortunately Churchill and the UK General Staff talked sense into the USA leadership in pointing out it would be some time before the USA had the ground and air forces for such a venture, or the transport shipping and landing craft needed. Among other issues such as lack of training or actual combat experience for USA forces.
Settling upon an initial attack on the fringe of Axis expansion via North Africa landings/invasion turned out to be a blessing in disguise as the USA quickly learned in the next few month it's many shortfalls in training, organization, and combat experience. Not a few set ot lessons, that would take many months ~ year plus to sink in. But enough to realize that a late 1942 landing on mainland Europe would have been a large scale disaster.
Still, as the campaigns of North Africa showed a resolution on the future, there recurred talk of landing in Western-Central Europe sometime in 1943. Again our British allies counseled caution and "not yet" which was begrudgingly accepted by the USA leadership.
With Sicily a "short" hop from Tunisia, the Allies/USA settled on that as the next objective. Following the Axis evacuation of North Africa/Tunisia and as a measure to further clear passage for shipping between Gibraltar and Suez.
After subduing Sicily, "toe" of Italy was right there and another "hop" over to go for. Alas, the Italian mainland is a narrow and long peninsula with a mountainous core and thin bands of coastal low, flat lands on West and East side. Not much room to engage maneuver warfare tactics for flanking thrusts, the campaign up the 'leg' of Italy was terrain favoring the defender and quickly degenerated into a replay of WWOne trench warfare tactics. A literal 'meat-grinder' for the US and UK troops.
Fighting overland northward up Italy would be slow and costly, so by January 1944 an amphibious flank move was tried with a landing at Anzio. Unfortunately, this "end pass" move was too short beyond the main German line of resistance and quickly blocked by German forces seizing the high-ground around the Allied beach-head, aided by the slow advance of the Allies off the beaches and inland. A might have worked plan that was poorly executed, resulting in major forces trapped for months before being able to break out.
For the most part, Western Allied(USA & UK) campaigning in the Mediterranean ~Italy-Balkans-Greece-(Eastern Europe) was a slow and costly way to attack Axis and Nazi Germany's "soft underbelly".
One option that might have had a major effect at this point in the war would have been to reduce forces on the Italian mainland to a defensive "hold" line of a handful of divisions and instead of a landing at Anzio, do one to the south of France. Thsi would not be the quick drive landing into Paris or Germany, but would have bypassed the gridlock of the Italian geography and been the sort of "deep pass" drive that would be a serious and major distraction to the Axis ~ Germany. It might even have drawn off forces that would be used in Northern France a few months later when Overlord~Normandy landings would have been held.
As for the major/main plan of landing in France, northern coastlines were desired for closeness to Germany and also the prospect of short shipping supply lines and closeness to land air bases to provide air cover. An essential to any large scale amphibious landing operation is the ability to seize and provide major port facilities to offload supplies and reinforcements. Also closeness to land airbases for effective overhead air cover helps, especially since most of the large fleet aircraft carriers are involve in the Pacific part of the war.
While Calais would seem a good place given it being the closest to England, that also made it too obvious and an area of some of the largest German defense efforts/entrenchments. Normandy stuck a balance of being one of the slightly further away locations yet not too far to make a good strike out point for liberating France and driving towards Germany.
While Stalin was pressuring the West ~USA and UK~ to "open a second" front closer to Germany, the main West incentive was to take pressure off the threats to England while liberating as much of Europe as possible and prevent too much from falling into Soviet hands. While FDR and Churchill wanted to work "with" Stalin, they also had their own agendas at odds with Stalin and the goals of international Communism, so it's not quite accurate to say they were Stalin's puppets.