Big dogs brands rest surprisingly (2,8)

I believe the answer is:

st bernards

I'm a little stuck... Click here to teach me more about this clue!

'big dogs' is the definition.
'st bernards' can be an answer for 'dogs' (I've seen this before). I am not sure about the 'big' bit.

'brands rest surprisingly' is the wordplay.
'surprisingly' indicates an anagram (a surprising ordering of the letters).
'brands'+'rest'='brandsrest'
'brandsrest' is an anagram of 'ST BERNARDS'.

Can you help me to learn more?

(Another definition for st bernards that I've seen is " Dogs".)

I've seen this clue in the Sydney Morning Herald.

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