That is a crazy amount of driving. I would definitely choose one or the other, as most of the stretch from NF to Montreal is long and has nothing to see. But then again, I would have 3 kids in a mini-van. Neither are exactly ideal for an "exciting" road trip.
The falls themselves are beautiful, but the surrounding area has a very "tourist trap" feel about it. If you do a google image search of Niagara Falls Ontario City, you will see what I mean. If that's what you are guys are looking for, great! But I doubt you will find any Asian markets close, though. Also, you have to pay to park everywhere - it is expensive, and they aggressively ticket.
I don't have much experience with Montreal, as I've only been there once for a training seminar. Lots of history, dining, and culture - but driving in town is a NIGHTMARE. Literally get some blood pressure meds if you go.
If you still want a "multi-city" vacation, from Montreal, it is only a 2 hour drive to Ottawa or a 2.5 hour drive to Quebec City. Both are rich with history, and Ottawa has some great museums and markets.
