The US did contemplate a 1942 invasion of France, but it was aimed at the Brest and Cherbourg. It's codename was Sledgehammer as The Red indicated. It was considered as an option in case the Soviet Union collapsed, or was close to collapsing, in 1942. However, it was not a realistic plan and was not a real option.
Operation Torch was the alternate plan. FDR was insistent that the American Army fight the Germans in 1942 somewhere. It was hoped that by taking French North Africa that the Free French forces would gain new recruits and become a sizable contigent of the Western Allies. It would also eliminate the Axis from Africa, secure the Meditterranean, and threaten the Axis throughout southern Europe.
An invasion at the south of France (I assume you mean Vichy France and not German occupied Bordeaux) would accomplish some of those goals, but not all, and would have very different risks. It wouldn't insure that the Axis would leave North Africa. It would not be as effective at securing the Mediterranean Sea. It would also keep the US and UK forces separate and able to be defeated in detail (which would assuredly be done to the US in France). It would also risk that all of Vichy France would defect to the Germans in a way that an invasion only of French North Africa would not.