All the info is on the St. Lawrence seaway web site:
Vessel maximum: 225.5 m (740 ft.) length; 23.77 m (78 ft.) beam; 8.08 m (26 ft., 6 in.) draft
; 35.5 m (116.5 ft.) height above water.
check Seaway System - The Seaway - Facts and Figures
You will need to start worrying about bridges in the Montreal area. You will need to call the CP bridge (VHF 68) to have it open as well as the two bridges in the Valleyfield area (West of Montreal). You can have the bridges status here Seaway System - Seaway Bridge Status
For the water level, tide and currents check this page Tides, Currents, and Water Levels
Let me know if you need help with locks in Montreal.