Healthy number taking in Montreal's centre (6)
I believe the answer is:
strong
'healthy' is the definition.
(thesaurus)
'number taking in montreal's centre' is the wordplay.
'number' becomes 'song' (I've seen this before**).
'taking in' means one lot of letters goes inside another.
'centre' means to look at the middle letters.
The middle of 'montreal' is 'tr'.
'song' enclosing 'tr' is 'STRONG'.
(Other definitions for strong that I've seen before include "Vigorous" , "Convincing" , "Intense" , "Resilient" , "is excelling" .)