I know that there are good days and bad, but would you generally advise risking it for a long weekend, or postponing if you think the chances we’ll be stuck inside all day are too high?
Where i live there was one day where it was very smelly disgusting outside. I know Montreal got it harsher, but still. That specific day i still did my daily walk, it was worst in the morning but more tolerable later in the afternoon, still not pleasant but have to do what i gotta do. Basically if you plan on enjoying bar terasse and other convenience of Montreal then i guess these specific times may not be the best ever. But if you wanna come to have bedroom fun... whats the issue really. Plenty of indoor places to finish the night ...
wear a decent mask and you'll be fine if you are staying outdoors but most don't wear one even when it was the worst out
otherwise, stay indoors and have fun
I have no underlying health conditions and i spent more than 8+ hours outside everyday during my trip
Make sure to check the aqi (air quality index) and wear a n95 or better mask to filter out the small particulates (check particulate size and whether or not the mask can filter it so you don't waste money)
If you really want to be super careful or you have some underlying health conditions, there are more specialized masks that can filter out very fine particulates like p100 paint masks.
You might look a little weird but who cares, health comes first.