Essentially, Canadian shivered into the period before Christmas (6)
I believe the answer is:
advent
'the period before christmas' is the definition.
(advent is the period leading up to Christmas Day)
'essentially canadian shivered' is the wordplay.
'essentially' says to take the centre.
'shivered' becomes 'vent' (I am not sure about this - if you are sure you should believe this answer much more).
The middle letters of 'canadian' are 'ad'.
'ad'+'vent'='ADVENT'
'into' is the link.
Can you help me to learn more?
(Other definitions for advent that I've seen before include "Period in the Christian calendar" , "Church season" , "Run-up to Christmas" , "when the Christmas shopping has to be done?" , "The coming of a religous period?" .)