Picking up son in YYZ en route from YQB to AUS on AC
 

My in-laws live in Toronto, and we are thinking of leaving my son there while we go to Quebec. I've already purchased the flights to return to AUS from YQB (AC1793 -> AC597). We have a 1.5 hour connection in YYZ and I'm trying to figure out exactly how the connection works so we can pick him up as we connect in YYZ. He's 9 years old, and Air Canada told me that if he is transiting security alone (or with his grandparents), he'd need to be registered as an unaccompanied minor, even though he'd actually be flying with us.

I understand from Air Canada's website that we need to go through security again in Toronto, but what I can't figure out is if the security described on that page is a bypass security or if it is the same security as someone departing from Toronto would take. And is the "US Connection Hall" different from the main CBP area? If they are different, how would one go about fully exiting to meet someone, and what would be the time impact on doing so.

We all have Nexus.

Thanks for any advice / thoughts.

The easiest way to do this would be to exit landside upon arrival from YQB and get your son and go through US customs and security together... 90 minutes could be tight if your flight is delayed and then your son is SOL. Any earlier flights from YQB-YYZ to which you could change to give yourself a longer window ?

If he is registering as unaccompanied minor and AC brings him to the gate, then you could theoretically all make it but if you misconnect, he would be flying to AUS by himself.

I will take a shot at this and others will add/correct. You are hightly dependent on your YQB flight arriving at YYZ on time.
You can exit at YYZ, pickup your son and head thru US CBP clearance. However this is tight since you have a 1.5hrs to exit and then go back after finding your son. Nexus will help big time. If you have checked bags at YQB, these get held till the US CBP releases them when they check you - this is what happens in the US Connection hall mentioned. I am not sure and would not be surprised is they will not let you exit while your bags are in transit - technically you could exit but US CBP could give you are hard time when you try getting back in. Also there is no enough time to short check your bags to YYZ, pick them up and recheck them.
If you have no bags, this is the best option. You deplane in YYZ, exit, pick up your son and then enter security (Nexus line) and US CBP (Nexus) thru the main hall. If there are 2 of you then put the bags under one person who would connect thru the connections hall and clear the bags while the other would exit to pick up your son.
Hope this is clear.

If you do split up and go through CBP separately, make sure whomever has the kid also has a consent letter from the other parent that gives permission to travel with the child alone.

Oh, thanks for that. We will definitely get that letter.