"Both are playing really well," Leach said. "They both are very similar in how they play."
The depth chart for the game lists either Tuel or Halliday starting.
Leach said last Saturday that if the game were to be played that day, Tuel would start. Tuel also took the majority of reps with the first team during training camp.
Tuel threw for 2,780 yards with 18 touchdowns as a sophomore, the one season he stayed healthy. He missed most of last season with a shoulder injury. Halliday stood out as his replacement until a lacerated liver ended his season.
Leach won't be rotating both quarterbacks.
"I can't think of very many people who have done a good job of that," Leach said. "With rare exceptions, I can't think of many teams that were very good at it."
Quarterbacks need to get into the rhythm of a game, and they see and evaluate the field better as a game goes on, he said.
Leach sat out the past two seasons after he was fired at Texas Tech, and the game at BYU, which is his alma mater, marks a return to the sidelines.
He has admitted being a bit nervous about being rusty.
"I'm anxious about the first game too," Leach said.
To prepare, Leach called plays from the sidelines during practices to simulate game situations.
Leach said he has seen plenty of film of BYU.
"We've watched 13 games' worth, to the point where we're really not interested in seeing blue Cougars," Leach said. "We're only interested in seeing red Cougars."
This being the eclectic Leach, he also has admitted to being impressed by the surfing skills of BYU coach Bronco Mendenhall.
"Probably one of the more interesting things about Bronco is that he's a really good surfer, and so getting some points of view from him on that subject is interesting," Leach said. "Bronco's an interesting guy and does a lot of interesting things. I'd be more interested in talking to him about surfing than football at this point."
Leach took Texas Tech to 10 bowl games in his 10 seasons before he was fired in a controversy involving a player with a concussion. He was hired by WSU last November to replace the fired Paul Wulff.
Leach said the offensive line has shown the most improvement since he has been with the Cougars.
"I think it's also the area where we had the most room to grow," Leach said. "We've got a lot of really young guys, kind of young unsung guys that I didn't know that we necessarily would be talking about that are in the mix."
Washington State went 9-40 in four seasons under Wulff, including 4-8 last year. Long-suffering fans have heaped expectations on Leach, with many hoping the Cougars qualify for a bowl game this season.
"I think that we're pretty capable," Leach has said. "I think our players had a really dedicated offseason, worked incredibly hard."
"But the whole `where are we at?' I don't know," Leach said. "I wish I could tell you."