The most common and most likely answer to this crossword clue is the 8 letter word BARGEMEN
I've seen this crossword clue in The Daily Telegraph
B
A
R
G
E
M
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N
More clues leading to the result BARGEMEN
Buddy explains!

The straight part
We know that "Canal workers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case canal workers = bargemen.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BARGEMEN mean?
BARGEMEN noun- A member of the crew of a barge.
- A barge owner, maintainer, or captain of a barge.
- A large white maggot that frequently infested ship's biscuits; most likely a larva of the cadelle beetle, Tenebroides mauritanicus.