As far as I know the B=>C airside connector is still not open yet and you'll have to reclear security.

I took one poor quality photo of the Terminal C side of the connector about 5 weeks ago - it looked like a construction site more than a gate area: https://photos.app.goo.gl/mSpTwCBdH9n5vDf98

When B=>C does open, you'll be able to walk all the way from Terminal B part 1 to Terminal B part 2 to Terminal C to (transiting the former AirTran terminal D) to Terminal E, which means you can visit the Air France lounge while flying United!!!

Tossup between walking and taking a shuttle bus landside B=>C; traffic and shuttle bus capacity can be frustrating sometimes. The walk is not too far, but it is a little tricky (follow signs or ask for directions and you should be ok).

I have spent most of the pandemic largely grounded but, every couple of months, taking the toddler to BOS landside as a treat, and walking among the terminals and showing them the planes. Getting into and out of Terminal B can be a little confusing depending on how you do it, but is not too bad if you read carefully.


p.s. tip for Cape Air: be the first one to board and they'll let you sit next to the pilot. fun/scary!