There is so much in Montreal that would be perfect for a mini-moon.
Walking around the Old Port can really feel like Europe. And all the amazing restaurants usually have incredible lunch deals. Definitely Check out Verses Restaurant and Modavie - two fantastic places.
The botanical gardens can be fun, and there is always the Biodome if you want to see some animals (the Penguins are so cute).
There is the underground mall, I think its 10KM of stores. There are little gem boutiques all around for different things depending on what you're looking for. There is this place on Crescent St. where I get Prada shoes for $120, and Hugo Boss suits for under $200.
There are a huge mix of hotels for every budget. Please PM or email me if you need some suggestions. Since most brides use hotels as getting ready locations for photos I have been to a lot of them.
I'll end here, but since I'm from here I could go on and on. If you need any more info on Montreal please contact me, I'd love to help.