In the summer Bowness Park located in NW Calgary offers a multitude of things to do. The park offers a spray pool for the kids to cool off, mini golf, picnic areas, bbq pits and both canoes and paddle boats to rent.
It's $15/hr per canoe and $20/hr per 2-person paddle boat. The man made lake has a fountain in the center and a number of off-shoot streams to paddle on.
If you don't have a chance to make it out to Banff, (or even if you do!) another great way to enjoy the natural beauty of the area is to rent a canoe at the Glenmore Resevoir and head out along the river. My favourite canoe trek is to head west towards Cochrane. Make sure to pack a lunch and some snacks. There will be ideal spots along the way for a nice (romantic!) picnic. Enjoy!!
To see some pictures of the reservoir, check out:
p.s. If you'd rather take in the view while floating and not 'paddling', another option is to rent a raft at Bowness River and lounge along the area there. This website offers information on the amenities and how to get there.