Same plane turnaround in YUL to/from the US
 

I'm trying to position myself to YUL in order to start an international itinerary. Both segments will be on AA(LUS), same plane with a turnaround time of 35mins. I know MCT is 1hr/1:30. However I'm wondering if it would be doable, without luggage of course. I know I need to use the US pre-clearance. I've transited in YVR before and the experience was rather quick and painless.

Does anyone have experience with connecting to the US? Are the formalities rather extensive or could I get through in 15-20minutes? Any thoughts or suggestions would be greatly appreciated!!

You will need to go through Canadian Immigration and Customs, go land-side, then pass through US pre-clearance (immigration, customs, security). Even if you have access to NEXUS (more or less a Canadian version of Global Entry) I don't think 35 mins is enough.
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13F

Is there a way to make direct transit without having to clear Canadian customs?

No. It is not possible when arriving from the US and returning to the US. If arriving from US and leaving on an International flight, there is a simplified immigration process, but still no direct transfer.
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13F

There is no way to do a Trans border to Trans border transit. You will have to clear CBSA entry procedures, U.S. CBP pre clearance, and CATSA security screening before boarding your next flight. Highly unlikely in 35 minutes.

AA rules require pax to be at the departure gate no later than T-30 from international (including Canada) departures. While AA won't generally offload you at T-30, if the flight is overbooked and at risk of oversale, AA will do so to prevent IDB/VDB.

As others note, there is no way to prevent entering Canada and then going through US pre-clearance. CBSA will be expedited, but nonetheless a process. No such thing as "transit" as might exist in some countries.

Thank you all for your responses! Knowing its a "simplified" process, what does that entail? Would it require going landside?

Same plane turnaround in YUL to/from the US
 

It is only simplified if you are connecting to an international flight, you will still have either the NEXUS, APM, or booth to go to for CBSA since you are terminating and starting a new journey in Canada. There is no way around having to enter Canada to be able to re-enter the US at YUL and stay airside, the system is not built for what you are trying.

The simplified process is for Intl-Intl or US-Intl. You have an immigration screening, but you stay airside.

But for any transit from International or US to a Canadian or a US destination, you must go landside.

Ouch. I originally had a backup plan of taking the next flight back(couldn't include in original itinerary due to several minutes below MCT in PHL). Just realized the flights are constantly delayed, now I'm inclined to not risk it since I'm connecting on an international flight.

Thank you all again for your insights!