That's been the focus at training this week according to big man Dunamis Lui, who is expected to return to Canberra's starting side on Sunday night pitting him head to head with returning Bulldogs prop Dylan Napa.

Canberra refers to their middle defence as the 'front door', and coach Ricky Stuart has been desperate to slam it shut all week after conceding a season-worst eight line breaks in Saturday's win over the lowly Gold Coast Titans.

Leading the Canterbury charge on Sunday will be a fired-up Napa who missed last weekend's loss against the New Zealand Warriors through suspension, found guilty for having 'led with his head' in a tackle against Wests Tiger Moses Mbye.

"When they get through our middles they're coming through our front door, that's one area we like to protect, we're doing a lot of work on that this week," Lui said.

"It's not a real big problem and I know we'll fix that real easy.

"He [Napa] is a real aggressive player, we all know that. They've been looking forward to getting him back too.

"We had a couple of slip ups last week in defence so that's going to be a real focus for us this week. With him coming back that's going to make that challenge a whole lot bigger for us."

Lui came from the bench in Saturday's 36-16 win over the Titans, his 150^th at NRL level, with Stuart deciding to start regular interchange trio Ryan Sutton, Joseph Tapine and Corey Harawira-Naera.

Josh Papalii was injected on 21 minutes, and Lui followed soon after adding plenty of starch to the Raiders pack.

Canberra will be without Harawira-Naera on Sunday, who isn't allowed to play against his former club.

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Meanwhile the Bulldogs have dropped English import Luke Thompson, who is reportedly homesick and struggling to adapt to life in the NRL bubble after recently shipping out from St Helens.

Reports surfaced this week that Thompson's girlfriend had been unable to join him in Australia, due to international restrictions in place to reduce the spread of COVID-19.

Despite the Bulldogs managing just two wins this season, playmaker Kieran Foran has hit a purple patch of form which has led to an upturn in recent Canterbury performances.

Three of their last four matches have produced losses by six points or less.

"He [Foran] is a real general in their team, if we can do a good job shutting him down we'll do a good job on the rest of the team," Lui said.

"Every game we go into it's always going to be a tough game. It doesn't matter who we're facing, we know we need to turn up it's not just a matter of making an appearance. It's another one of those games where we can't get too complacent, we need to be on the top of our game this weekend."