Hey Katie, Montreal is a good place to spend a birthday!
For your long run you can easily run 10 miles on Mount Royal. It's not that steep, but if you're not used to hills, it might be a little much. Check out the Olmstead trail on Mount Royal (it's the main gravel road) on a short run and see if you can handle the incline for 10 miles.
Otherwise the Lachine Canal is a great option. A nice place to start and finish is the Atwater market with its fruit and vegetable stands, bakeries, ice cream counter, chocolate makers, cafes, etc.
For bike rentals you have a lot of options. You can go here
, near the Atwater market, or here
or you can try your luck with our public bike system
for short trips.Mont Saint-Bruno
is a great place for a long run too. It's about 30 minutes from downtown Montreal. Mont Saint-Hilaire
is also a great place to run or hike. They have a good range of steep and not so steep trails. It's about a 45-minute drive.
For rafting, stay away from the St-Lawrence tourist traps. You should google "Riviere Rouge" for the real thing.
Some folks on this board used to run together on Thursday evenings, but that has died out. There may be some other groups out there if you're looking to run with people. Or you can try any one of the Running Room stores.