Ahoy! You can complete the declaration through the ArriveCan app up to 72 hours in advance of flying into Canada. Once you arrive down in to the customs hall you'll see the express lanes that are exclusive to those who have completed the advance declaration. I think the signs are green and should be towards the left hand side as you enter the area. Go to the eGates and scan your passport, get a receipt and show it to the CBSA officer. Assuming all is well, you'll go through the baggage hall and hand the receipt to the final officer prior to exiting. You won't need to enter the reference code as it's attached to your travel docs.