There's several issues which limit the size of a display in Montreal. Firstly, there's the container in which the fireworks are shipped - this can only hold so much! Secondly, there is the time it takes to set up all the mortars etc. on the actual site in the time available - there's 2 days for fusing and pre-mounting and 3 days out on the ramps actually setting up.
In a display, a company could, if they wanted to set everything off all at once - but that wouldn't make a good display. So there has to be a balance between the finale and the rest of the show. It could be that 25% of the total number of shells fired are in the finale. But care has to be taken that this is in proportion to the rest of the display. Also, sheer volume of shells fired is not always the best indicator of the visual and aural impression such a barrage gives. Tools like Alberto's visualization software can help in this regard. Alberto did a fabulous demo of this software at the Symposium. Even the "amateur" version, PyroCreator, is very impressive since it uses the same particle animation engine that the pro tool uses. I have a copy of this and have had a lot of fun designing displays with it. More info can by found at
http://pyroinfinity.tv
Anyway, back to the topic. There are practical limits to what can be fired in Montreal which are really dictated by the time needed to set up the display, not really by any rules on the loudness or brightness of a finale. The only other limit is that no shells of larger calibre than 12 inches can be used.
Paul.