As explained by Enkil, Notre-Dame offers a wonderful and efficient view of the fireworks outside of La Ronde. While the bridge is also at a good advantage for witnessing many low effects, some of the fireworks themselves (low and high level) may be hidden because of the bridge being at an angle nearly perpendicular to the firing site.
Notre-Dame is a good secondary choice because it is, as already mentioned, almost like a mirror, if you will, to the firing site (with the exception of seeing the very low effects and proximity to the site itself). Of course, I advise that you do indeed view the fireworks from the park as your primary choice fpr the greatest benefits, but outside of the park, I would point my fingers to Notre-Dame. The ramps are not visible from Notre-Dame, but it's not difficult to pinpoint which ramps the fireworks are coming from.
Trav.
