Currently, everyone only flies wide-body aircraft.
Air Canada operates YUL-EDI and YHZ-LHR on 737s, and WestJet operates YHZ-BCN, YYZ-EDI, and YYZ-DUB. And that's not even counting the dozens of flights to and from KEF (which might or might not count as TATL depending on whether you consider Iceland to be in Europe or in the middle of the Atlantic).
PHL to EDI is further than the AC and WestJet flights, and I wouldn't count KEF as transatlantic. I'm not aware of any US carriers flying narrow bodies across the Atlantic. American has an old US Air Hub in Philly, so I imagine that is why it is from PHL.
Air Canada operates YUL-EDI and YHZ-LHR on 737s, and WestJet operates YHZ-BCN, YYZ-EDI, and YYZ-DUB. And that's not even counting the dozens of flights to and from KEF (which might or might not count as TATL depending on whether you consider Iceland to be in Europe or in the middle of the Atlantic).