First off, shooting a handgun at the range and actually hunting with one is completely different!! I'm certainly not passing judgement on you, but you need to know what you're getting into before taking a "handcannon" afield. I'm a die-hard pistol hunter, but my Dad wouldn't let me go after deer until I learned the responsibilities that go with it. I started out with a 22lr hunting squirrels and after I showed him that I was responsible with one and could make a quick and humane shot , he finally let me move up to bigger game. The last thing we want, as responsible sportsmen, is a wounded animal running around.
Now with that said and if you still feel like you can make us pistol-hunters proud, and if your parents will allow it, go with the Ruger 44mag. With you being from Maine, I guess the bears you'll be hunting are black bears and the 44 is plenty enough for them. Its cheaper to shoot, less recoil and it has way more factory and handloads. The S&W 500 will cost you almost twice as much to buy versus the Ruger, the 500 ammo is too expensive and I think that its just too much for what you want to hunt. "Overkill" only costs you more meat damage!!
As for the laws that go with handgun hunting in Maine, you need to check with your DNR or a local warden. Like I said above, I'm not passing judgement on you, I just wanted you to take into perspective some of the things that come with pistol hunting. Good luck and I wish you the best.