I'd do:
Fly into Boston
Fly to BUF
Fly to NYC (or DC)
Train to DC (or NYC) and then Fly out of DC.
You'll be burning too much time driving otherwise and during the winter the area is isn't so scenic I went to University in Buffalo and grew up near NYC so I've done the drive many times. In good weather you can make it speedy. With any snow on the roads you'll be slowed. The best route requires suing some smaller roads but they cut out ~40 minutes.
For flight pricing you may wish you add a day or two (or just do 1 day in Niagara) and fly into Toronto on AC to YYZ or PD to YTZ. I really enjoy Toronto and in the winter, while cold, it's an interesting city with a great combination of cultures.
Avoid parking fees in Washington & NYC as much as possible. The hassle & costs plus the tolls you'll pay in addition will add up quickly.
Also, Philadelphia and Baltimore are great cities between DC & NYC.
Last edited by Yoshi212; Aug 11, 2017 at 12:44 am