Where to see the fireworks from
To get to La Ronde, take the metro to Ile Ste Helene and follow the signs to La Ronde. Reserved seats start at around Can$32. Access to the site only (no rides), but with good viewing costs around Can$16.
Another good vantage point is from the foot of the Jacques Cartier Bridge on the Montréal side of the St. Laurent river. Take the metro to Papineau and walk to the junction of Rue Notre Dame and Avenue De Lorimier. There is a good view of the river from here. This is easy to find since there will be many other people heading in that direction on firework evenings.
Alternatively, the Jacques Cartier Bridge makes a good vantage point since it is closed to traffic. Access is from Avenue De Lorimier by heading NW (this is referred to as "North" in Montreal).
Finally, there are some viewing points in Old Montreal, but in my opinion these are not too great since they are too far away to hear the bangs properly. The Jacques Cartier bridge can also be accessed from Ile St Helene itself.
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