Mr Thompson said Palmerston North police were working with Interpol "to put the necessary alerts in place" and eventually have him extradited back here to face court.
The detective was shocked at what had been alleged in Canada.
"The nature of the charge comes as a surprise to us, put it that way."
Farley had taken "extensive steps" to evade capture, including obtaining a false identity. "It would be very rare for someone to go to the lengths he has ... and we're equally determined that he wasn't forgotten."
He skipped the country the same morning he took his e-bracelet off.
"So that takes some pre-planning."
Inspector Laurence Rankin, in Canada, said Farley had been "picked up" this month by Canadian Border Services Agency for violating immigration laws. He was subsequently investigated as a suspect before being charged with the March 4 offence against the sex worker.
"We knew we had a particularly horrific case of kidnapping and we wanted to take every step possible to find the attacker," Mr Rankin said.
Media in Canada said officers alleged the 42-year-old victim was picked up against her will, driven to a secluded area, tied up and beaten. Witnesses called 911 as they watched her being dragged behind a white van down a city street.
Police believe the woman partly freed herself and, fearing for her life, tried to jump from the moving vehicle.
The woman, who has since been released from hospital, suffered serious injuries, including to her head, but was able to give a description of her attacker.
Farley is charged with eight offences, including aggravated sexual assault, assault causing bodily harm and kidnapping.
- Additional reporting APNZ