Viv, I am so very sorry about your health issues. There's never a good time to face that but in the midst of wedding prep for your daughter it must have been particularly stressful and emotional. I'm so glad that treatment is finished for now and I wish for you a full recovery. A trip to Montreal seems just the ticket.
You look absolutely stunning in those photos, happy and glam, and your daughter's dress is so romantic and elegant.
Some suggestions for shopping and food while there.
Laurier Ave in Outrement. You'll find a La Canadienne flagship boutique there as well as the more reasonably priced Sandwich, which LaPed already mentioned. This is for high end boutiques. You can find others down on Sherbrooke Ave.
The Old City -- for a few unusual boutiques with local stuff as well as some designer shops, for jewellery, scarves, etc. There are also some vintage stores in the area.
Boulevard St. Laurent has some really interesting and funky spots. M0851 for leather.
For a different department store to what you know, check out Simon's.
Shopping will be end-of-summer stuff --- August is hot there -- so there won't be much fall stuff available yet -- but you might get a deal or two. Your dollar will go far and there is no tax on clothing, so even if it is something for next summer, you could consider.
I recommend a visit to the Musée des Beaux Arts. There is usually something interesting there and the restaurant is lovely for a lunch.
We've had some terrific meals at Damas.
Classic Montreal is L'Express. The food ranges from sensational to just okay but it's usually solid, and it really makes you feel you're in Quebec.
Most restaurants in the Old City are overpriced and not very good but there are a few exceptions. Here's a list of some good options (city wide): https://montreal.eater.com/map.....n-montreal
Some specific suggestions:
https://www.mtlblog.com/best-o.....-boutiques
http://www.likealocalguide.com.....-montreal/
Have a wonderful trip -- enjoy!