It wouldn't need cheek guns TM, they were equipped with four fixed guns in the nose fired by the pilot
Oh, I know about the Sunderland's cheek guns, it's just that they were piddly .303s. I'm thinking 4 x .50s or maybe 2 or 4 x 20mm to really put a beating on the deck crew and maybe actually damage the hull.
By the end of the war the U-boat crews got really good at riding the bubble to allow super quick dives. Sneaking up on them low, throttled back and relatively quiet and then hosing them with 20mm AP rounds would make a world of difference. The .303s, not so much.
The 20mm rounds would get there significantly before the plane could pass over to drop depth charges. The BAT would be much better, of course.
And the 20mm would make a much bigger mess out any small surface targets like barges or E-boats.