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No, you only have to clear customs. When connecting to another flight in YUL, you will bypass the main customs hall and be directed to another customs hall. As of June 2023, there still seems to be some ongoing work, especially regarding wayfinding and final construction of corridors. For passengers arriving from the US or EU, duty-free alcohol will not be an issue as you will have already cleared security.
The only exception to this would be if you have to retrieve your checked baggage as that is still done at the edge of the customs area for the main customs hall. You would only need to do this if your baggage won't be transferred automatically.