Don't bother with ArriveCAN... it's unnecessary and essentially dead. Oh, it never did provide any 'skip the line' benefit, it was a COVID-19 pre-screening tool.
If you're flying into Canada with the connection in Toronto (at least with Air Canada), you follow the signs to the connection gates (very well marked) and you'll go through a pretty quick and painless check with CBSA before making your way to the gate for your connecting flight. No need to worry about your luggage, it should have been routed to your final destination at your departure point. You're unlikely to find yourself in a crowd at immigration... most people arriving in Toronto go to the regular immigration/customs hall but you, as a connecting passenger, are split off from that herd.