Some play is normal, depending on the camera/lens combo. Nikons seem more prone than Canons. If the mounts are not physically loose on either the body or lens, not much can be done, other than just replacing the flanges and see if it improves things. As lenses are mounted/dismounted, the plating wears on the flanges and the interface will loosen over time.
Haven't seen this effect Canons much, but can lead to communication problems with Nikons. Tweaking the lens in one direction or another will oftentimes correct it.