Here's a cool Ottawa-based site that lets you estimate the cab fare between two locations. It's called Taxi Me. For example, the cab fare from City Hall on Lisgar Street out to Scotiabank Place is about $55.77.
From their blog: "TaxiMe calculates the distance between any 2 points using Google maps. When you punch in the starting and ending address, TaxiMe will show you a list of cab contacts in that city and estimate how much your trip is going to be."
Related: Ottawa Driving Guide