The first thing I have to say about Empire de l'échange/Exchange is that they have an adorable tumblo http://empire-exchange-mtl.tumblr.com
Second, the shop is really fantastic. Much like their sister stores Annex and Local 23 they have a really well organized and sorted collection of items. They obviously take care to ensure that what they're bringing in is in good quality and looking for a good home.
It also didn't feel super picked over. They obviously are bringing in stock all the time, so it felt like I was looking through a lot of great, diverse items. Which is exactly what you want in a vintage shop, I think.
The other thing that really impressed me is that they have a good selection of sizes and styles. There are party dresses and sweaters, cowboy boots and heels and really everything in between.
The woman working was lovely and helpful and chatted a bunch with us about good things to do and see in Montreal.