Reasoning the son is away travelling in Canada (6)
I believe the answer is:
regina
'in canada' is the definition.
('Regina' is part of 'canada')
'reasoning the son is away travelling' is the wordplay.
'is away' indicates named letters should be taken away.
'travelling' indicates an anagram.
'reasoning' with 'son' removed is 'reaing'.
'reaing' is an anagram of 'REGINA'.
(Other definitions for regina that I've seen before include "Queen (in lawsuits)" , "in Canada" , "Queen (Latin)" , "Title of reigning Queen" , "Reigning queen's title" .)