I think I can chime in as I live about 45min from Niagara Falls, so I know the area very well. I'd agree with Shawn that Niagara is a beautiful place to visit if you have never seen it. It has some lovely parks and lots of the really cheesy touristy stuff and they charge and extra 3% to all the fools who don't complain about the extra fee and refuse to pay it.
I have visit Montreal quite a few times as well. You are taking your life into your own hands driving in Montreal. The traffic lights are their for decorative purposes only. Sidewalks are fair game for motorists, but they do have some really nice art galleries and museums.
Montreal is a good 7 hours from Niagara. It's about the same time as it takes for you to get from Boston to Niagara.
I would consider taking a detor into Niagara on the Lake.. If you like wine, there are about 100 of them in the area.
http://www.niagarawineryguide.com/niagara-wineries-city/If you want to visit a Chinese Market, then I'd just go to Toronto and go up Spadina St into China Town. You can find just about anything there. Just below it is the fashion district where you can get fur coats. just east is the CN tower and Hockey Hall of Fame. And Toronto is just 1.5 hours out of Niagara. Then head north for 2.5 hours and visit Axiom.
