Key man in the canal trade? (4-6)

'the canal trade?' is the definition.
I know nothing about this answer so I can't judge whether this works.

'key man' is the wordplay.
I cannot quite understand how this works, but
'key' could be 'e' (a musical key) and 'e' is located in the answer.
'man' could be 'lock' and 'lock' is found in the answer.
This explanation may well be incorrect...

'in' acts as a link.

Can you help me to learn more?