Afghan police officials said it appeared that Monday's blast, which left a 1.5-metre-wide crater beside a busy road in eastern Kabul, was caused by a powerful remote-controlled bomb.
Interior Ministry official Abd al-Ghafur, who was at the scene, confirmed that one Canadian was injured, but said the car's Afghan driver and a translator were unharmed.
Afghan police cordoned off the scene of the blast as Nato troops surrounded a red four-wheel-drive vehicle. Several of its windows were broken by shrapnel and a small Canadian flag could be seen on the bumper.
An official from the Canadian embassy, speaking on condition of anonymity, said the victim was a male security guard.
No claim yet
The official did not identify the man and had no information about the extent of his injuries, although witnesses said he walked unaided from the damaged vehicle.
"It looks like a main charge was placed by the side of the road" and detonated as the vehicle drove by, Warrant Officer Neil Reeve, a member of the British contingent of the Nato force sent to investigate, said.
There was no immediate claim of responsibility for the blast. However, US commanders have warned that Taliban fighters may step up attacks as the harsh Afghan winter recedes.
The Canadian embassy lies on a busy road running between US and British military bases.