The International Fireworks Competition is always a fun affair!  This year the festival runs from July 1st to August 1st on Saturdays and Wednesdays.  Officially it is run by Laronde and with a ticket to the amusement park on a fireworks day you can get up close and personal to the fireworks.  You don't have to spend all that money to enjoy them though.  At the old port is a great place to view them as well as on mount Royal.  You can even enjoy them with the music by tuning into 105.7 FM.
The fireworks usually start at 10pm and last half an hour.

https://www.sixflags.com/larondeen/linternational-des-feux/program