Rizzo and Bryant were announced as part of the field on Wednesday. It will be held at Great American Ball Park in Cincinnati the day before the All-Star Game presented by T-Mobile.
"We're just going into it to have fun," Bryant said. "Cincinnati is such a good hitter's park. I get to watch [Rizzo] every day in [batting practice] and it's pretty special. Hopefully, I win it, but if he wins, that's great, too."
They're the first Cubs to participate in the event since Sammy Sosa did so 2004. Sosa won it in 2000.
Rizzo leads the Cubs with 16 home runs, Bryant has 12 in his rookie season.
"I prefer that they both win," Maddon said. "If there's such a thing as a tie and they both win, I'll take it."
The Cubs manager had said he'd prefer neither take part, but acknowledged that both were excited about the chance.
"I knew their preference," Maddon said. "I think they'll handle it properly. If there's ever been a tie for the winner, I'd like it to be this year."
Rizzo and Bryant will compete along with the Reds' Todd Frazier and two-time champ Prince Fielder of the Rangers. Others in the field include Blue Jays third baseman Josh Donaldson, who was MLB's leading vote-getter for the 2015 All-Star Game; Orioles third baseman Manny Machado; Dodgers rookie outfielder Joc Pederson; and three-time NL MVP Albert Pujols of the Angels.
This year's event will introduce a new streamlined format featuring brackets and timed rounds. Brackets in the first round were seeded based on 2015 home run totals through Tuesday's games. The first-round matchups will include No. 1 seed Pujols vs. No. 8 seed Bryant; No. 2 seed Frazier vs. No. 7 seed Fielder; No. 3 seed Donaldson vs. No. 6 seed Rizzo; and No. 4 seed Pederson vs. No. 5 seed Machado.
Bryant, the sixth rookie to compete in the Derby, will have his father, Mike, a former Minor League outfielder in the Red Sox system, throw to him, while Rizzo will try to get an edge with Cubs coach Franklin Font.
"I'm looking forward to experiencing that with my dad -- not many kids can say they had their dad pitch to him in the Home Run Derby," Bryant said.
Said Rizzo: "It's going to be exciting. Kris and I will really enjoy it; I think everyone that will participate will enjoy it. It's something I watched growing up as a kid, and participated in a few, and it's going to be awesome."
Rizzo has hit six home runs in 88 at-bats over 23 games at Great American Ball Park; Bryant has none in two games there.
"It's going to be fun [to go with Bryant], just soak it all in," said Rizzo, who is an All-Star for the second straight year. "I'm going to do the same thing [as last year] and enjoy it. You never know if you'll ever go again, if anyone will ever go again, so just have as much fun as you can."
The two planned to discuss some hitting strategy before the Home Run Derby. Bryant's father throws batting practice to him in the offseason, so this won't be anything new, just a bigger stage.
"It's batting practice, so we'll have fun with it," Rizzo said.