Several things to ask: how are you travelling, alone or with somebody. As well, what is your age and what exactly are you looking for: sports, sights, nightlife, and so on. What one person finds interesting, the other may not and vice versa. (As an example Niagara Falls, one of the wonders of the world, just south of Toronto is awesome and if you have a girlfriend with you, she'd love it. Yet, single teenage males may find it boring.)
To get some more info, you might want to post your message on the Toronto and Boston and NYC boards or even the main board as well to get more insight. As well, you could check out the Quebec and Ontario travel sites.
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As an added note, I live in Montreal but do sports trips to Toronto several times a year ... what I usually do is leave Montreal Friday morning by train for an NBA Raptors game on Friday evening and then again on Sun afternoon and an afternoon MLB Blue Jays baseball game on Saturday or Monday. If I am really lucky I can get a hockey game on Saturday evening but usually I just visit friends or relatives on Saturday and normally go out for dinner. To include baseball, it has to be done in April when you are going. (If I just do NBA games, I come back Sunday, then it only needs one workday.)
A good combo and when I'll be going is Sat Apr 04th evening Raptors, Sat 05th afternoon Blue Jays, Sat 05th evening Leafs game, and Sun 06th afternoon Blue Jays against Yankees. That way I lose only one workday and take the train back to Montreal on Sun evening. I get all three major sports that way and all within walking distance of the train station.