The most common and most likely answer to this crossword clue is the 7 letter word CAMPING
I've seen this crossword clue in The Guardian
C
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More clues leading to the result CAMPING
Buddy explains!

The straight part
We know that "holidaying under canvas" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case holidaying under canvas = camping.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 CAMPING mean?
CAMPING verb- To live in a tent or similar temporary accommodation.
- To set up a camp.
- To afford rest or lodging for.
- To stay in an advantageous location in a video game, such as next to a power-up's spawning point or in order to guard an area.
- To fight; contend in battle or in any kind of contest; to strive with others in doing anything; compete.
- To wrangle; argue.
- The recreational activity of temporarily living in a tent or similar accommodation, usually in the wilderness.
- The act of setting up a camp.