Pe@rson From United Kingdom, joined Jan 2001, 19373 posts, RR: 52 Posted (4 years 10 months 6 days 5 hours ago) and read 4668 times:
I’ll be flying LHR-YYZ-BWI-YYZ-LHR in late December by the 333, DH1 (x2), and 763. The 763 is scheduled to operate YYZ-LHR. While it’s not overly important, will the 763 feature AC’s new interior and seatback IFE? It appears it will based on this*, but I thought I’d double-check.
Also, will I need to clear security in YYZ en-route to or from BWI?
Coming from LHR to BWI you will go through security after US pre-clearance (actually avoiding Canadian immigration entirely).
Going to LHR from BWI I think you get a simple passport check and are allowed to stay in T1 and be able to go to your gate for the flight to LHR. You might get a small check but not the same thing that you would get if you were checking in at YYZ,