A few years ago, I was YUL based and flew to the US frequently. The process went as follows:

Check in at airline, tag checked bags. Carry tagged bags to the pre-clearance area. Pass through Duty Free (and buy what you wish), wait in line for customs & immigration (still with checked bags in hand), clear customs & immigration, drop off checked bags on carrousel, go through security, enter terminal and go to gate.

My uncle and I were having a debate about this tonight, and he insisted the process has now changed to the following:

Check in at airline, tag checked bags. Drop off checked bags onto carrousel. Go through security. Go through immigration (not exactly sure where customs happens since he says your bags are already gone), get to terminal (where Duty Free is located).

Who is right?