MSP-BOS will be your best bet, plenty of flights between JB, DL and Sun Country. Your only choice will be 190BOS

DFW-BOS is not as easy. We have 2, sometimes 1 flight a day, something they get cute and put an e190 on it. The flights schedules between AA and JB aren’t that great.

DEN-JFK... 1 redeye on JB, lot’s of commuters, LGA as backup.
DEN-BOS, 2 flights on JB, one redeye.

I feel DEN has lots of commuters to anywhere, and people living West of DEN tend to commute thru there a lot.