I do not know any tours to Niagara Falls departing from one city and returning to another. Also, it is unlikely that any tours would be provided by any tour company in March. That is in the off season when few tourists venture to Niagara Falls.
Fortunately, the Greyhound Bus Company, our major interstate bus company in the USA, offers bus trips to and from most major cities. The Greyhound web pages are located here. It appears that they offer three trips from Boston to Niagara Falls Ontario every day. The same bus company offers ten trips from Niagara Falls Ontario to New York City every day. It should be no problem taking a bus from Boston to Niagara Falls, then taking a bus from Niagara Falls to New York City.
It should also be quite easy to obtain hotel accommodations in Niagara Falls, Ontario or in Niagara Falls New York. The prices should be rather reasonable in March as the tourist season does not begin until May.