Niagara Airbus is a rather expensive alternative, for a roundtrip for a couple of people.
Check out the rail fares on VIA Rail Canada besides the Amtrak fare. VIA has several trains a day from downtown Toronto to Niagara Falls (be sure when checking the schedules that you look for Niagara Falls, Ontario, rather then Niagara Falls, N.Y, across the border), and the round-trip fares are quite reasonable, especially if you can book a few weeks in advance, or can qualify for a seniors fare. Use your search engine to find the VIA Rail website. If you take the train back to Toronto, the cab or limo from Union Station to YYZ will probably be in the $50-55 CAD range.
The other alternative is to rent a car for a few days. It's an easy drive to NF, with travel time usually less then 1 1/2 hours each way, traffic and rush hour permitting. This would allow stopovers in Niagara-On-The-Lake, with its interesting shops, hotels, and nearby wineries, and it's only about 15 minutes drive from NF.
Hope this helps. Have a good trip.
bj-21.