Physically yes, technically not a chance. Firstly the iPad 3 has a quad core gpu and all that jazz and obviously the retina display. A huge difference.
Apple throwing in tech no dev will use for at least the next 2 years. I went from an iPad 2 to a 3 and see it now as a waste of money. Same can be said about the iPhone 4 to 4S. Different tech but nothing there to use it to justify the upgrade. Hopefully the iPhone 5 wont be iPad 3 tech in a smaller case.