Metal unknown in Canada, at first (4)
I believe the answer is:
zinc
'metal' is the definition.
(zinc is a metal)
'unknown in canada at first' is the wordplay.
'unknown' becomes 'z' (algebra).
'at first' says to take the initial letters.
The initial letter of 'canada' is 'c'.
'z'+'in'+'c'='ZINC'
(Other definitions for zinc that I've seen before include "Sivery-white metal" , "Antioxidant element" , "White metallic element usedin alloys" , "Blusish-white lustrous metallic element" , "Anti-corrosion agent" .)