Pulze Scene Manager is your friend here. Admittedly it would be better if it was native to Corona so we didn't have to pay for another piece of software but hey ho
The ability to set render resolution per camera has been requested many times in the past but is still needed. This could also include a dropdown menu with resolutions/aspect ratios presets and the option for the users to save their own presets.
But since Vray has implemented this to its cameras, this could be very helpful in Corona too, as well as a Proportion GuidesHope this could be implemented soon