It sort of depends on your layover in YYZ. If it's less than a couple hours, there's an offhand chance something might go missing, although on LHR-YYZ-YXE I've only had it happen once, and they had it out to me 24 hours later.
YMMV, but it seems to depend more on the connection in YYZ than anything in my experience, although it's gotten better since mainline service came back to YXE.
Have a great trip, though, and might I recommend Cafe Sola (downtown next to the bus depot, but not as bad as the location would suggest) if you have some spare time and might be needing some caffeine?