'I've heard a few versions of this song and Martin Simpson's version is the best in my opinion.... However, one thing I've always wondered: is this the same melody as Banks of the Bann?'

That's a good spot, it is indeed. However, I'm slightly puzzled: that tune sounds exactly like the one to which Nic Jones sang 'The Lakes of Shilin' (and I agree with Dave Sutherland's post from five years ago that his live performances of it were sensational), but MS sings different words and calls it 'Lake of Champlain'. But I played guitar on Sara Grey's recording of 'Lake of Champlain' many years ago, and she had a modal tune that was nothing like 'Banks of the Bann'. Curious.