Labor Day Monday - Niagara or DC? [closed]

I'm travelling with a colleague in US for the next week and cannot change schedules. From midday Sunday (4 Sep 2016) we need to travel with a rental car from Detroit to NYC until Tuesday afternoon. We were thinking of choosing one of these two for Monday: Niagara Falls or Washington DC.

Since we're both EU citizens it's quite an hassle to get the Canada visa just to save 2.5h of driving (and lose time at the border). We're unfamiliar with how that weekend plays out in terms of traffic but expecting a few hours of delay anyway.

Should we choose Niagara for Monday morning? If yes, how busy should we expect the ride 'Maid of the mist' to be (waiting times)? Any chance to book an air ride with Rainbow Air (the other helicopter ride is in Canada) on the spot or the day before?

Should we choose DC instead for Monday afternoon? Is it doable to spend the night in DC or closeby and make the drive in time for JFK until Tuesday 4pm?

Or should we drop both and go back to NYC which we've already visited?

Average driving times for reference, not sure how these will be affected: