Though I did not go on a tour of the Normandy sites -- I wish I had -- when I visited in 2012, I can offer one suggestion anyway. I rented a car and saw key sites, covering a lot of ground. I put 80 miles on the car. I rented from an agency in Bayeux across the street from my hotel. (Make sure to see the glorious Bayeux Tapestry, a war relic from nearly 1,000 years ago!)
The highlights include a museum in Arromanches about the invasion and logistics of it, the German gun emplacements about 15 miles away, Omaha, Utah and Gold and other beaches, Pointe-du-Hoc, the American cemetery, the German cemetery and other sites.
The highlight was Pointe-du-Hoc, where Americans shot grappling hooks into cliffs and ascended them under German fire. You can walk into bomb craters still very much visible. There's an underground German command post you can enter.
Two days should be enough. In addition to the D-Day sites and Bayeux sites, the World War II museum in Caen is worth visiting. There's a interesting medieval castle in Caen.
My dad was a US World War II vet, but he was on a destroyer in the Pacific. At Normandy, I met an 88-year-old US Navy war vet who was also in the Pacific from Texas. I wonder if he was a herald from dad, who died in 2006.