Canadian police have released CCTV footage of murdered Australian Lucas Fowler and his American girlfriend Chynna Deese, taken two days before their bodies were found.

Key points: The bodies of Mr Fowler and Ms Deese were found on the side of Alaska Highway on July 15

The bodies of Mr Fowler and Ms Deese were found on the side of Alaska Highway on July 15 Lucas's father, Stephen Fowler, spoke at a press conference over how "distraught" the family is

Lucas's father, Stephen Fowler, spoke at a press conference over how "distraught" the family is Police say the murders could be linked to two teenagers who have also gone missing in the area

Mr Fowler, 23, and Ms Deese, 24, are seen embracing alongside their van at a service station on the evening of Saturday, July 13.

Police said the footage was taken at Fort Nelson, a region within the Northern Rockies about 300 kilometres from where the bodies were found shot dead beside the Alaska Highway on the morning of Monday, July 15.

The couple are seen cleaning and filling up the van, and warmly embracing during the pit stop.

It comes as police continue to appeal for witnesses to come forward.

Mr Fowler's father, NSW Police Chief Inspector Stephen Fowler, made an emotional plea at a press conference in Canada on Monday evening (local time) for any information.

He said the pair were inseparable.

"It's a love story that's ended tragically. It really is," he said.

"It's the worst-ever love story."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 50 seconds 1 m 50 s Lucas's father, Stephen Fowler, has described how "distraught" the family are

Police said the murders could be linked to the disappearance of two teenagers who went missing 470 kilometres from where Mr Fowler and Ms Deese were found dead.

Kam McLeod, 19, and Bryer Schmegelsky, 18, were the drivers of a Dodge pick-up truck found on fire in British Columbia, at an area known as Dease Lake.

"It is unusual to have two major investigations undergoing of this nature in northern BC at the same time, and so we recognise that there is a possibility that these could be linked," said Royal Canadian Mounted Police (RCMP) spokeswoman Sergeant Janelle Shoihet.

However, Corporal Chris Manseau, another officer working on the case of the missing teenagers, cautioned that "at this point we don't have anything to link them".

Police have released a sketch of a man said to be one of the last people to speak to Mr Fowler on Highway 97 on the evening of July 14.

A sketch of a man who police say was seen speaking to Mr Fowler on July 14. ( ABC News )

He was described as Caucasian, with darker skin and dark hair, with a possible beard or glasses.

He was driving an older model Jeep Cherokee with a black stripe on the hood and a black bullbar and is believed to have been travelling south.

Corporal Shoihet said he was not a suspect, but someone police wished to speak to.

Canadians Bryer Schmegelsky and Kam McLeod have been missing since Friday. ( Supplied )

'We are just distraught'

Chief Inspector Fowler said he was hopeful the case would be resolved.

"As you know, I may have been an experienced police officer but today I'm standing here as the father of a murder victim," he said at the press conference.

"We are just distraught.

"This has really torn two families apart.

"Our son Lucas was having the time of life travelling the world. He met a beautiful young lady and they teamed up, they were a great pair and they fell in love.

"We were overjoyed for Lucas."

Canadian Police confirmed Chynna Deese and Lucas Fowler were both shot dead. ( Supplied )

He said the pair had then planned the trip to Canada and had communicated with the Fowler family as they were leaving.

"What happened after that, time will tell I guess," he said.

"We are hopeful of a positive outcome and obviously we're appealing along with the RCMP for anyone to contact [police] who may have any information whatsoever, however little, please contact the police."

RCMP released a map and appealed for witnesses to come forward. ( Supplied: RCMP )

With his voice breaking, he paid tribute to his son and Ms Deese.

"Lucas was just a fun-loving guy who had a goal to travel the world. He saved up all his money whilst he was working in Sydney. He set out on an adventure with a mate.

"Along that tour he met Chynna and they became an inseparable pair," he said.

"Two young people who had everything ahead of them tragically murdered."