The duo was rested for the team`s last league match against India in Chennai, where they lost by 80 runs.
Gayle was rested due to abdominal strain while Roach was down with viral fever and stomach infection.
Skipper Darren Sammy said both Gayle and Roach spent considerable amount of time at nets at the Sher-e-Bangla stadium today and expected them to recover fully before the quarter-final.
"I liked the way Chris was hitting balls in the nets," said Sammy.
"He is very committed to the West Indies cause. Come tomorrow, and I have no doubt both he and Kemar will play."
Sammy did not reveal if pacer Ravi Rampaul, who took five wickets against India in his first appearance in this tournament, will be retained if Roach returns to the side.
"We will assess the conditions and discuss it amongst ourselves before finalising the team," he said. "We will put out the best possible team which can deal with the conditions."
West Indies would look to bury the disappointments of losing two matches from dominant positions, against Shahid Afridi and his men.
Chasing England`s target of 244, they were cruising along at 222-6 before losing their last four wickets for three runs.
Against India on Sunday, they lost their last eight wickets for just 34 runs after being 154-2 at one stage.
The West Indies are yet to win a match against leading nations since 2009. They have now lost 18 successive matches against the established teams.
"We did lose our way and can`t keep collapsing like that all the time," Sammy said.
"And we certainly can`t do that in a quarter-final. But I am confident we can put the past behind us and hopefully the West Indies will win. It will be an exciting game."
The West Indies will be boosted by the fact that it was at this venue that they shot out Bangladesh for their lowest one-day total of 58 in the league phase.
"It is definitely an advantage to have played here earlier," said Roach. "We executed our plans well against Bangladesh and we will take confidence from that."
Sammy, however, knows that Pakistan is going to be a different ball game. They topped Group A with five wins in six matches, including a four-wicket victory of Australia.
The win ended the three-time defending champions` unbeaten streak of 34 World Cup matches over a 12-year period.
"Pakistan have been playing good cricket, especially Shahid Afridi who has led from the front. But we must focus on what we have to do to execute our plans and win the game.
"This is the quarter-final and everything depends on how we play on the day. It does not matter if you are number one or number eight. If you don`t win you are out."