I did YUL GE once recently so my sample size is small. There is a internal loooong corridor that takes you to US CBP. My time of day there was zero lineup. And despite clearing the GE machine US CBP still decided to ask me three questions. So based on my experience there would not have been any benefit to leave the secure area. My memory is foggy but i am not sure if I had to do security again prior to US CBP.