They begin their 2025 season in Perth, with Felix Auger-Aliassime and Leylah Fernandez headlining the Canadians at the third edition of the tournament from December 27th to January 5th.
Defending champions Germany, led by world number three Alexander Zverev, were pitted alongside Brazil and China, who have Olympic champion Zheng Qinwen.
Stefanos Tsitsipas' Greece will also play in Perth, grouped with Kazakhstan and a Spanish team missing world number two Carlos Alcaraz.
Alcaraz is yet to reveal where he will warm up for the Australian Open, the opening Grand Slam of the year.
Five-time major champion Iga Swiatek and Hubert Hurkacz once more represent Poland as they look to avenge their narrow loss to Germany in the 2024 final.
They face the Czech Republic and Casper Ruud's Norway in Sydney.
Like Alcaraz, world number one Jannik Sinner has opted against playing the United Cup for his country Italy, who will meet France and Switzerland in the group stage.
Britain take on Alex de Minaur's Australia in the other Sydney group.
"Everyone who plays this event absolutely loves the experience," tournament director Stephen Farrow said. "It's the perfect way to acclimatise to the Australian conditions."
Seven of the world's top 10 women and six of the world's top 12 men have signed up.
Each team - with three men and three women - go through a round-robin format, with ties comprising one men's and one women's singles and a mixed-doubles clash.
Group winners in each city advance to the quarter-finals, along with the best runner-up.
The semi-finals and final are in Sydney with $10 million in prize money and ATP and WTA ranking points at stake.
United Cup draw:
Perth
Group A: USA, Canada, TBC
Group C: Greece, Kazakhstan, Spain
Group F: China, Germany, Brazil
Sydney
Group B: Poland, Czech Republic, Norway
Group D: Italy, France, Switzerland
Group F: Britain, Australia, TBC
