There will be a lot of cross patching going on since I expect officers from outside of Boston to be in to assist. In the past BAPERN 3, one of the 8Tac91, the Federal Interop VHF, have all been patched together.
BPD 16 seems to be in use for crews set up barricades, which isn't that interesting.
I'd also listen to the MSP "Statewide" TG since the Air Wing operates on that. Boston EMS will be using a Tac channel, maybe Tac 5 or Tac 6 as well, I expect.
If Boston FD has anything going, I'd expect it to be on Channel 4. And the Transit Police may have units there as well as there are a couple of T stations nearby.