There are plenty of tours down to Niagara, just search with the words Niagra and Tours.
I did a trip in March 06 when there were lumps of ice going over the falls, that's why Maid of the Mist does not operate in winter. Transport was in a 20 seater bus with stops for wine tasting, at Niagra on the Lake and at Niagara Helicopters before going to the falls.
When it is cold outside a nice warm Bell 407 is the best way to go sightseeing.