What's the best travel option from Toronto to Ottawa on short notice? I guess Grey Hound or some similar bus agency would be it?
I've taken that bus(Greyhound). It's about $40 each way. You should get a bus with wifi and power outlets. It's about 5 hours and it has one 15 minute rest stop about 1/2 way through. Well if you get the Express one anyway. There are non express buses that stop in every hick town along the way.
You can also do Via, but you're not going to get a $40 fare on short notice, you need to book well in advance to get that rate.