AC in YYZ is under no obligation to check your luggage through. K on AC is a Tango Plus fare which does include 1 free checked bag so you might get lucky having a nice check-in agent who does interline your baggage which should then go to Tokyo since you preclear US customs at YYZ. Be nice and try but if they say no they're still right.
If they do say yes you will show them your printed itinerary for the next flight with PNR code. The time between the two flights is not enough for my comfort zone. I'd fly in the night before or if possible have at least 4 hours between flights.
You'll have to get your luggage at LAX either way as you do so at entry into the US. Ideally it would be tagged to YYZ so you can just drop it off for handling but if not you'll have to go to AC to check it in before heading to security.