Both the BRU and GVA flights operate as domestic segments on the YYZ/YUL/YYZ sectors. If you are traveling onwards internationally, you must deplane to allow for catering and grooming, and return to the same gate showing your passport prior to re-boarding the same aircraft. IIRC, these flights always operate out of swing gates 50 or 51 at YUL to allow for a combined domestic/international operation.