Bitterly cold in lorry crossing Canada's capital (6)
I believe the answer is:
arctic
'bitterly cold' is the definition.
'lorry crossing canada's capital' is the wordplay.
'lorry' becomes 'artic' (articulated lorry is a semi-trailer truck).
'crossing' indicates putting letters inside.
'capital' says to take the initial letters.
The first letter of 'canada' is 'c'.
'artic' placed around 'c' is 'ARCTIC'.
'in' acts as a link.
(Other definitions for arctic that I've seen before include "Freezing cold like North Pole" , "Northern ocean" , "Relating to the cold North" , "Relating to North Pole region" , "Area around the North Pole" .)