A little late to this thread, but I just did TLV-YUL-LGA and did not need to show anything transiting through Canada. However, I'd recommend doing YYZ on your return flight as they have later flights to NY area. We almost missed our YUL-LGA leg (6:45pm is last of the night, as opposed to an 8:30pm in YYZ) and I feel like we'd have been sleeping airside. Luckily they held the flight for us.