Alberta's highest court has upheld a 12-year sentence for a man who cut off his victim's thumb during an abduction.

Steven Vollrath was convicted in 2016 of kidnapping, aggravating assault, possession of a weapon and impersonating a police officer.

His victim, Richard Suter, was taken a year earlier from his Edmonton home by three masked men who tortured him and left him in the snow.

Suter was awaiting trial at the time for crashing his SUV into a restaurant patio, killing two-year-old Geo Mounsef.

The Court of Appeal of Alberta ruled Vollrath's sentence was appropriate, but a dissenting judge said he would have reduced the term to nine years.

Court heard that the abduction could have been a vigilante act, but there was no evidence to prove it or to connect Vollrath to the child's family.

"It appears that this was a revenge kidnapping that was well planned," said the Appeal Court's majority decision.

Richard Suter in hospital after being abducted and assaulted by Steven Vollrath. (Supplied )

It detailed how Vollrath purchased fake police-like gear and, with two others, went to Suter's home late at night.

They handcuffed the retired businessman in front of his wife, put a bag over his head and forced him outside in a bathrobe and boots. He was then driven to a remote location and forced to kneel in the snow, where his left thumb was amputated.

"The appellant and others left the complainant unconscious, bleeding and alone in a snowbank in the midst of a harsh Alberta winter," wrote the court.

"When the complainant asked his captors why he had been taken from his home and attacked, the only reason given was a reference to whether he 'hurt anyone last fall and whether the child died."'

Suter later pleaded guilty to failing to provide a breath sample in the death of Geo. He testified that he was having an argument with his wife when he mistakenly hit the gas instead of the brake and crashed into the patio.

Earlier this year, the Supreme Court reduced Suter's 26-month sentence to the 10 months he had already served behind bars.