Did YUL to YYZ and YYZ to LAS last week on a Friday mid-afternoon. Yes go up the escalator near gate D20. Went through security again but if you have GE or Nexus the whole thing took should take less than 10 minutes. I had to wait 2 minutes at customs since someone was in the wrong line. US Customs Officer showed me a picture of my bags and asked me what was inside. I was in the US MLL in less than 20 minutes from landing at D41. Overall the experience was fine and relatively quick and painless.