Flying out of Atlanta tomorrow on AC7543 (to Toronto).

I will have to return my car to the Rental Car Center..

Assuming I can get a mobile boarding pass, can I clear security at the dometic terminal which is connected to the Rental Car Center with a train. Or do I need to take a shuttle bus to the international terminal. I have no checked luggage.

Thanks in advance for any advice. I couldnt find a clear answer to this anywahere!