Olive & Gourmando is a cute brekkie/brunch spot with delicious pastries and dishes. Chia pudding is amazing. The fresh fruits and mango puree are a nice touch. The muesli adds a great crunch. Banana chocolate brioche is sweet but not overwhelmingly.
If the wait is too long, there were many people doing takeaway. So that is also an option.
I definitely recommend for brunch before exploring old Montreal.