The Brumbies are the only unbeaten side in the competition after they defeated the Western Force 25-10 on Friday, and can now secure a berth in the final with a win over the Reds.
While Chisholm and Shepherdson are expected to start in their usual positions at lock and prop respectively, Gerrard may be moved from the wing to fly-half.
And Gerrard has admitted that several players in the Wallabies side could benefit from playing out of position.
"While we have the depth in Australian rugby, we don't seem to have the experience in certain positions," he said.
"I'm looking forward to the challenge of playing closer to the action and getting my hands on the ball more often.
"But the most important thing is to continue the excellent work the team has already done (this season).
"The Reds had a good win over NSW at the weekend, so we'll definitely need to be on our game to beat them."
Chisholm also said that he was looking forward to getting some 'game time' during the Wallabies break between the Tri-Nations and the European tour in November.
"The most important thing for me is to get some games under my belt," he said.
"I've had time here and there (with the Wallabies) over the past few months, but I'm keen to play some more footy at a high-level throughout the rest of the APC.
"I'm not too fussed whether I play at lock or at number six. The team has found a winning formula, so I'll be happy to fit in wherever I can and contribute to the success of the side for the rest of the competition."