Brunch date on a Sunday morning...
I find most of the good brunch places are quite bustling rather than quiet & romantic...unless you go early (before 10ish). But some, like Lawrence, seem to fill up right from opening time. I think Reservoir would be fairly quiet earlier in the day. Maybe some of the fancier places would be a bit quieter but I wouldn't know.
(hope it's not too late)
If you want a quiet place for a first date, I'd stay away from the more "hipster" brunch places (lawrence, reservoir, chien fumant); they don't take reservation, and if you want to impress, you don't want to be caught with nowhere to eat.
For a first date with a great woman, I'd go to Lemeac.
as an alternative to lemeac which gets very busy at Sunday brunch you might consider Rumi in same neighbourhood. I went there today for Montreal Highlights special lunch deal (they were still serving brunch, serve it now daily Sunday til Thursday 11 am til 3pm, have unusual choices like omelette with dates) and found food delicious and varied. The service is friendly, decor mixed middle eastern, cozy neighbourhood place and quiet for conversation. They take reservations (front window area nice and more private) if you want to be sure . They even have a sectioned off two table area. Parking free on neighbourhood streets.
Heard great things about Lemeac on this forum so we decided to try it out this morning. We made reservations through open-table an hour before. It was marvellous! We enjoyed the food (and mimosas) and the service was impeccable. We will be back soon to try their after 10pm menu. Thanks for the recommendation Chowhounders!