See canny, here, is Northumbrian equivalent of "so nicely" or "so gently".
Terry laments the tendency for landlubber collectors to clean up verses through either a final verse admitting innocence or through making the hanging subjects guilty of their own crimes. Cecil Sharp, 1915, for example concludes his variant with "But I never hanged nobody".
Masefield gives a particularly sentimental accounting:
Another strangely beautiful chanty is that known as Hanging Johnny. It has a melancholy tune that is one of the saddest things I have ever heard. I heard it for the first time off the Horn, in a snowstorm, when we were hoisting topsails after heavy weather. There was a heavy, grey sea running and the decks were awash. The skies were sodden and oily, shutting in the sea about a quarter of a mile away. Some birds were flying about us, screaming.
The Chanty-man began. They call me Hanging Johnny,
The Sailors. Away-i-oh ;
The Chanty-man. They call me Hanging Johnny,
The Sailors. So hang, boys, hang.
I thought at the time that it was the whole scene set to music. I cannot repeat those words to their melancholy wavering music without seeing the line of yellow oilskins,
the wet deck, the frozen ropes, and the great grey seas running up into the sky.