1st Round Pick
Why Boston does it:
They need a PG ASAP to replace Rondo, and Lowry fits the bill.
Why Raptors do it:
They get a nice hall for Lowry, and remove themselves of Fields contract in the process. Melo and the 1st are pieces for the future, and Bass/Lee can be kept (and likely started) or sent off with other deals in the future.
This is just something I whipped together quick, what do you think?