BA 349 then AC 857 at Heathrow
Nice → London → Toronto
Timetable, London time
21:05BA 349 from Nice at the gate
15:00AC 857 to Toronto leaves the gate
17 h 55 apart on the timetable, overnight
AC 857 leaves 17 h 55 after BA 349 arrives on the timetable: more than half a day, so not a connection we count.