The wicket at Heritage Bank Stadium on the Gold Coast features a drop-in pitch.
"We are not sure how it will play so we want to see how it goes and give ourselves the best chance," McSweeney said.
There is also a slight chance of bad weather later in the evening.
The ILT20 competition in the UAE has impacted on the batting order of both squads. The Heat will be without Colin Munro and Sam Billings for the finals.
The Sixers have lost James Vince.
The winner of the clash will host the BBL final on Wednesday. The loser will host the winner of Saturday's knockout final between Perth Scorchers and Adelaide Strikers. That game, known as the challenger final, will be played on Monday.
BRISBANE HEAT: Jimmy Peirson, Josh Brown, Nathan McSweeney (capt), Matt Renshaw, Max Bryant, Paul Walter, Michael Neser, Xavier Bartlett, Spencer Johnson, Mitchell Swepson, Matthew Kuhnemann.
SYDNEY SIXERS: Jack Edwards, Daniel Hughes, Josh Philippe (wk), Moises Henriques (capt), Jordan Silk, Joel Davies, Hayden Kerr, Sean Aboott, Ben Dwarshuis, Todd Murphy, Steve O'Keefe.
23°C