If for some reason you see someone you know, they will probably be just as surprised to see you, as you them. Just quietly explain to them you are not out and they will probably respect your wishes....
Hopefully you are not flying in on day of departure. Currently YYZ is getting bad press for horrendous customs delays. I would guess AC has multiple daily flights to Quebec City, and if you miss your connection you will be accomodated on later flight.