whimsey, my first choice would be BOS via MUC to CDG on LH, because MUC is much more convenient for connecting flights than FRA (itīs a long way to go…). As I do not like to clear immigrations & customs more than necessary, AC is the third option:

Option 1 (9h 55 min)
LH 425 (340) BOS-MUC 17.45-0810+
LH 5734 (CR7) MUC-CDG 09.05-10.40

Option 2 (9h 25 min)
LH 421 (340) BOS-FRA 20.40-10.45+
LH 4088 (32S) FRA-CDG 11.55-13.05

Option 3 (9h 50 min)
AC 387 (CRJ) BOS-YUL 16.30-17.40
AC 870 (333) YUL-CDG 19.30-09:20+