Donnelly gets his first start for more than a month and replaces Josh Bekhuis, who moves to the bench. Cowan comes into the team in place of Aaron Smith, who put together a disappointing performance against the Waratahs last week.
It will be a meeting of two sides on losing streaks, the Blues having lost their last four games while the Highlanders have also slumped to defeat in their last three games.
Despite those losses, the Blues are still in the playoff hunt but the Highlanders kissed goodbye to the playoffs with the defeat by the Waratahs last week.
Highlanders coach Jamie Joseph said the side's integrity was at stake and there was a need to finish the season in style.
"Obviously we are keen to go up there and show our wares. It has been a long season but nevertheless the guys are pretty happy with the season and want to finish off well," he said.
"The big thing for us this week has been resting. It was quite a physical game and we did a lot of travelling, having to travel back to Australia, and the body needs to recover. And mentally you need to recover."
The side had just one training run this week, a short, sharp one yesterday, as the side looks to finish with a better than 50% winning record.
Joseph said having a player of Donnelly's ability and experience coming back for the final game of the season was a plus for te team.
Donnelly has had a mixed year and will be struggling to get back into an All Black jersey but a good performance tomorrow night will not go unnoticed by the three wise men.
"He is an All Black and shows that he is a quality player and I'm expecting a lot from him," Joseph said.
"The thing we are playing for is to make sure we finish on a high note. No matter whether we win, lose or draw, we have to play well, and we have our personal integrity to maintain."
The side was no more tired than any other side and every team was aware it was a long season.
"They realise it has been a long season but they are also aware they want to go out there and get a win for the team."
The match will be for the Gordon Hunter Memorial Trophy and Joseph said that was an incentive to play well, to get the trophy back after a long spell away.
"I think it's something like six years since we've held it and Whopper [captain Jamie Mackintosh] spoke it about it today and what it means to us.
That would be a good way to end the season, coming home with that." The Blues have more or less qualified for the playoffs but a win tomorrow night should also confirm a home game in the first week of the finals.
Former Otago and Highlanders halfback Chris Smylie will make his first start for the Blues this season, taking the place of Alby Mathewson, who suffered a head knock in the loss to the Crusaders last Saturday and has struggled to train this week.
In the other change to the Blues, utility Lachie Munro comes on to the left wing, with Rene Ranger gone for the season after straining his hamstring last week.
Highlanders v Blues, Auckland, tomorrow, 7.35pm
The teams
Highlanders:
Ben Smith, Matt Saunders, Kendrick Lynn, Shaun Treeby, Siale Piutau, Tony Brown, Jimmy Cowan, Nasi Manu, Alando Soakai, Adam Thomson, Tom Donnelly, Jarrad Hoeata, Chris King, Jason Rutledge, Jamie Mackintosh (captain).
Reserves: Mahonri Schwalger, Bronson Murray, Josh Bekhuis, Nick Crosswell, Aaron Smith, Robbie Robinson, Telusa Veainu.
Blues: Jared Payne, Joe Rokocoko, Benson Stanley, Luke McAlister, Lachie Munro, Stephen Brett, Chris Smylie, Peter Saili, Luke Braid, Jerome Kaino, Ali Williams, Anthony Boric, John Afoa, Keven Mealamu (captain), Charlie Faumuina.
Reserves: Tom McCartney, Tevita Mailau, Chris Lowrey, Sean Polwart, Alby Mathewson, Winston Stanley, Sherwin Stowers.
