The Brumbies are aiming to break the Chiefs' two-year unbeaten run in the Super Rugby play-offs when they clash in a grand final rematch at Canberra Stadium on Saturday night.

Winger Clyde Rathbone is battling to be fit while rookie prop Allan Alaalatoa will be thrown onto the Brumbies' bench for his debut against two of the biggest front-rowers in Super Rugby.

The Chiefs came from behind to beat the Brumbies 27-22 in the grand final last year but Alexander said the Brumbies buried their demons when they beat the Chiefs on Anzac Day this season.

"It's been and gone, even if we win this game, it won't make amends for [losing the final]," Alexander said.

"The only way you can rectify a grand final loss is to win a grand final. We have to win this game, but as far as holding anything from last year, it went on Anzac Day. We just want to progress to next week."

The Brumbies will face a significant size disadvantage when props Alexander and Scott Sio line up against Ben Tameifuna and Jamie Mackintosh.

Tameifuna is the Chiefs' 137-kilogram wrecking ball who can destroy opponents in open space and the scrum while Mackintosh is 130 kilograms.

Brumbies lock Scott Fardy said the key to limiting Tameifuna's impact was making him do extra work around the field to take away from his explosive running game.

Alexander said the Brumbies would use technique to combat the size difference.

‘‘Yeah, they’re very big guys - you’ve just got to find ways around that using technique, work ethic and what not,’’ Alexander said.

‘‘Sides have scrummed well against them, and then they’ve touched up other sides as well.’’

Alaalatoa will get his first cap from the bench after Jean-Pierre Smith injured his knee against the Western Force last weekend.

It has forced the Brumbies into a big-man reshuffle with Ruan Smith covering as a loosehead prop and Australian under-20s prop Alaalatoa backing up Alexander at tighthead.

Brumbies director of rugby Laurie Fisher had no hesitation throwing Alaalatoa into the qualifying final cauldron, even though it means he's squaring off against Tameifuna and Mackintosh.

Alaalatoa will become the 37th player the Brumbies have used this season after being hit with a massive injury toll.

"I reckon [Alaalatoa] will do a fantastic job when he's called on. I really enjoyed his scrummaging this morning and he has a fantastic attitude," Fisher said.

"He's grown a lot since he's been with us; he'll be that excited and buzzing he'll do a great job. Allan's not small, he won't lack for size, but he might lack for experience."

Rathbone, Robbie Coleman and Joseph Tomane are jostling for a wing and bench spot.

Rathbone has started the past two games, while Coleman missed the win against the Force with a hip problem and Tomane made a successful comeback from a broken jaw.

BRUMBIES FAN DAY

Wednesday: Brumbies players including Ben Mowen, Henry Speight, Pat McCabe, Ben Alexander, Scott Fardy and Nic White will be in the Canberra Centre signing autographs from 12.30-1pm.