We flew Toronto through Atlanta with delta down & back a year ago. Coming home we had about 2 1/2 hours in Atlanta airport. We did not have to collect luggage Sxm had tag on it for yyz. We did go through u.s. customs with carryon . No time at all. Lovely dinner at One Flew South restaurant in Atlanta airport. The waiter asks when your flight is so they know how fast they need to be. Very well organized. I love our 4 1/2 hr direct flight but if we had to go through u.s. again we would go Delta through Atlanta again.