Maintaining a field of 2T is no small order. It would also have to maintain relative position as Mars orbits the sun. Its an interesting idea. I doubt Mars has or ever had the chemical composition to become human-habitable but it's a good idea to do as much as we can the easiest way possible. It would help support other efforts but you'll need more than an artificial magnetosphere. Mars' gravity can't support 100Kpa.
Send the robots to beam pictures and data back. By the time we get out there we won't need to breathe or eat anymore. We won't need to terraform.