I don't know if there's automated way of doing this, but if there's not very many cameras in your scene, you can "convert" them manually. To do this, first switch to the camera view in the viewport, then press "p" to switch to perspective and in Corona toolbar press create Corona camera from view. The new camera will be placed at exactly the same position as the old one and their field of view will be matching. Keep in mind that the new camera will not inherit more advanced effects, like exposure, shutter speed, DOF, etc. - you'll have to re-create these manually.