It's on.

Canada's prime minister has accepted a challenge from Montreal Canadiens' star defenceman P.K. Subban to sing a Christmas carol for children in hospital and post it on Twitter.

Subban threw the challenge his way on Thursday, via Twitter.

"Hey Justin Trudeau! You have great hair, but can you sing Jingle Bells?" Subban said in a tweet from inside the Bell Centre.

On Friday afternoon, the prime minister responded, saying he was going to make it a family affair.

"You're about to find out, P.K. Subban. Sophie and I are warming up as we speak," Trudeau tweeted back.

Canadians immediately weighed in on social media.

The goal of the Subban-fronted campaign is to create a country-wide social media singalong to brighten up the holidays for kids at the Montreal Children's Hospital and other pediatric hospitals.

Earlier this year, Subban's foundation pledged $10 million to the Montreal Children's, and the new hospital named its atrium in his honour.