Coach Tony Smith said Kenny-Dowall - who scored four tries in 19 games last year - was a "pretty obvious choice" and confirmed Minchella, 24, is being schooled as a future captain.
Both players will be in their second season at the club and Kenny-Dowall, 33, took up the leadership role last year following Mose Masoe's career-ending injury and in the absence of Weller Hauraki, who has now retired.
Minchella, who began his career at Leeds Rhinos, was Rovers' players' player of the year in 2020.
Smith admitted Kenny-Dowall's appointment was not a difficult decision.
"It's a pretty obvious choice within the way he leads us and the respect he earned from all of us throughout the whole club," he said of the New Zealander.
"That's not just about what he's done prior in his career and even last year, it's just the manner in which he conducts and applies himself, along with the amount of effort he puts in."
Smith added: "By his own admittance, he would have like to have played better last year, but it wasn't through a lack of effort.
"I've had good conversations with him about it, that some overseas players struggle in their first year and don't hit the heights they would like to or have before. They often settle into that second season and become more solid.
"I'll also say to anybody out there that when asked about the pressure of captaincy on top of performing, he said that ‘there's pressure anyway’.
"He is the right person to be our leader and he was happy to put his hand up and accept that and he is very honoured."
Of Minchella, Smith said: "It's a reward for how he has approached his time here and I think it is a show of respect for what he has earned.
"That role is also a case of Elliot being shaped into his future as well.
"He's a big part of developing young people and young men.
"We don't see it as just a case of the older players being captains; I think young people could be great leaders, it isn't just down to experience, it's down to how you handle yourself and how you can encourage each other to become better.
"He certainly leads the way in that respect."
Smith stressed: "The other thing that really stands out about Elliot is that he is prepared to say what he thinks.
"He'll give an opinion and ask questions.
"He's not worried about what other people might think about him asking that question or making that comment.
"I think that's great leadership to the younger people behind him.accepted that."