The most common and most likely answer to this crossword clue is the 8 letter word LABRADOR
I've seen this crossword clue in Financial Times
L
A
B
R
A
D
O
R
More clues leading to the result LABRADOR
- Political reformer enlisted by US socialists in area of N America
- Boy embraces supporter winning gold in Canada
- A drab role largely at sea for man’s best friend
- City supporter setting up bar somewhere in Canada
- Work for American touring terrific area of Canada
- Note support and stick up for Canadian region
- Hound extremist during work in US
- Gatecrashing two parties, artist with lead on rescue dog (8
- Live rough abroad, on river, with dog
- Item worn by Madonna in French Canadian region?
Buddy explains!

The straight part
We know that "man’s best friend" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case man’s best friend = labrador.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 LABRADOR mean?
LABRADOR noun- A Labrador retriever.