They stood at attention as the young soldier's casket was lifted aboard a Hercules transport plane, which will arrive in Canada by Tuesday.
Twenty-three-year-old Longtin, of Longueuil, Que., died Sunday when his light armoured vehicle struck a roadside bomb.
About 1,100 members of the Van Doos -- the popular name for Quebec's Royal 22nd Regiment -- are currently serving in Afghanistan.
"Everybody's morale is low but at the same time, like we say, it's motivating us (to continue)," Jean-Philippe Auclair of 3rd Battalion, Royal 22nd Regiment told The Canadian Press.
"For sure, we're never going to forget him and he will always be with us."
Support for the Afghanistan mission is lower in Quebec than any other province, according to recent polls.
Peter MacKay, newly appointed as Canada's minister of defence, spoke to soldiers Monday in Valcartier where the Van Doos are based.
He said Canadians are fighting to make Afghanistan a peaceful place, as the military has done for other war-torn countries around the world.
"Know that this mission is no less important, no less valid and takes no less valour," he said.
Friends of Longtin told CTV Montreal that he believed in the mission and remained optimistic that NATO would achieve its goals in Afghanistan -- a sentiment echoed by Auclair.
"I still believe in the mission and it's motivating me even more to keep going. Simon was aware of the risks, he knew what he was doing and I'm sure he wouldn't regret anything," he said.
Auclair added he wants Quebecers "to be better informed" about Canada's objectives in the country before passing judgment.
Another Van Doos member and friend of Longtin, Scott Bernier, told CTV News that Canadian soldiers will continue to fight for stability in Afghanistan.
"We are here to do a job. And even if Simon's not here, we will continue to do it for him," he said.
Quebec-based military personnel currently make up almost half of Canada's 2,300 troops in Afghanistan.
Auclair is travelling aboard the Hercules transport plane with his friend's casket, and will attend Longtin's funeral.
He said it will be difficult for him to meet with Longtin's family and friends -- especially the slain soldier's girlfriend.
"That's going to be hard. Those two were so much in love," he said
Col. Juneau said the death will hit the Van Doos hard."It's like losing almost a brother. We're like a big family here," he said. "We will mourn, we will pay our respects to the family and our fallen comrade, and we will carry on with the mission. The important thing for us, the soldiers, the whole team that is deployed here, is the fact that we know the Canadian public is behind the soldiers, the people wearing the uniform," he said.