Hello happygolfer.
Check out this link. It is a discussion from this forum which took place a few months ago, and it has quite a bit of information on hotels near Union Station in Toronto.
http://www.tripadvisor.com/ShowTopic-g155019-i55-k728366-Overnight_in_Toronto-Toronto_Ontario.html
As far as Niagara Falls, there are several bus tours that leave Toronto for Niagara Falls. There is also always the option of taking the train from Toronto to Niagara Falls and then you could take a taxi to Niagara on the Lake when you are ready to leave the falls, then you could make your own plan. It is a very short drive maybe fifteen minutes or so from the falls to Niagara on the Lake. If you do want to take an organized bus tour there are several companies that offer tours from Toronto to Niagara Falls.
The first link here is to via rail for train information and then the other links are information related to bus tours.
http://www.viarail.ca/trains/en_trai_onta_toni.html
http://www.niagaratorontotours.com/
http://www.tripadvisor.com/ShowTopic-g154998-i97-k582246-Niagara_Falls_from_Toronto_with_time_in_NOTL-Niagara_Falls_Ontario.html
On the left side of the page, of the following link there is a list of several tours to Niagara Falls.
http://www.niagarafallstours.net/tours/tourtype.cfm/ttid2/3539?ovchn=ggl&ovcpn=bus&ovcrn=niagara+falls+bus+tours&ovtac=ppc
In Niagara Falls do not miss the Maid of the Mist. In my opinion it is absolutely the highlight.
http://www.niagaraparks.com/nfgg/maidmist.php
http://www.niagarafallslive.com/Attractions_in_Niagara_Falls.htm
In Niagara on the Lake, there is a gorgeous downtown area with some nice little boutiques, a few antique shops, an art gallery/store and restaurants. There are also many wineries in Niagara on the Lake plus a dinner theatre. It really is a great place to spend an afternoon.
http://www.tripadvisor.com/SmartDeals-g154999-Niagara_on_the_Lake_Ontario-Hotel-Deals.html
http://www.niagaraonthelake.com/
Hope this will get you started.
Best of luck.
n/d