I'm not sure exactly what time the Wonder pulls into Port Canaveral, but I believe it will already be docked by then. When the ship is docked, the Space Center is on the Port side of the ship and you can easily see the tall outline of the Vehicle Assembly Building from the Wonder. You should have an amazing view of the launch from the Wonder, and you should also be able to hear it really well, too.
About seeing the launch from the Magic:
Thursday is an At Sea day and you would have just left St Thomas on Wednesday evening. I think the distance from Port Canaveral would be too great for you to see anything from there.