The standard Sunderland had ten 303s in three turrets, with the option of two 303s or 0.5 in guns in the side hatches. A few crews also fitted four fixed 0.5 in guns in the nose for strafing U boats. It turned very tightly for its size, using its very effective flaps. In RL it was mostly up against big long range LW aircraft like Ju 88s or Condors which it could outmaneuver. However a slow, mostly 303 armed aircraft it is not going to be very survivable in the MA.
The Catalina would be a better flying boat to introduce. Although not any more survivable it would have a lot more scenario potential. It was used by the US, the British and the Soviets and far more widely than the Sunderland. It carried torpedoes as well as bombs and depth charges and later versions were amphibious.
For the MA a flying boat could be enabled at ports which would give it some sort of reason for being used as opposed to a land based bomber. A conventional early war twin engined bomber like a He111 or similar would be more useful scenario-wise though.
