However, Barnes said there were so many "big hitters" in the United States that their inclusion skewed the competition.
"I don't agree with opening up the Booker for the Americans. I think that's straightforwardly daft," he told the Radio Times.
"The Americans have got enough prizes of their own. The idea of [the Booker Prize] being Britain, Ireland, the old Commonwealth countries and new voices in English from around the world gave it a particular character and meant it could bring on writers.
"If you also include Americans - and get a couple of heavy hitters - then the unknown Canadian novelist hasn't got a chance."
Barnes asked: "Which American prizes are open to Brits? In theory I think only the National Book Award is. I don't think any Brit has won a major American award for years."
Barnes is not the only author to criticise the decision.
Australian writer Peter Carey, who has won the Booker twice, previously criticised the decision to open up the award.
"I find it unimaginable that the Pulitzer or the National Book award people in the United States would ever open their prizes to Brits and Australians," he said.
"There was and there is a real Commonwealth culture. It's different. America doesn't really feel to be a part of that ... I suppose I'm not generally in love with the notion of global marketing."
Barnes also said that he was now on civil terms with fellow writer Martin Amis, with whom he fell out when Amis parted ways with Barnes' wife, Pat Kavanagh - who later died in 2008 - as his agent.
"When we meet, we talk," he said of Amis. "It's not a problem. He lives in Brooklyn and I live in Tufnell Park."
Barnes is also still impressed with the standard of literature, both in Britain and beyond.
"Writers and publishers are like farmers. It's always a bad year. And the internationalisation of literary fiction, the boom in translations, is all to the good.
"The literary novel does things no other art form can. To speak heart to heart, and mind to mind. One to one. To have that voice, whispering in your ear. In the quietness of your room. Telling you things about the heart, mind and soul. That can't be done half as well elsewhere."
Barnes admitted he only allows his agent to send him the "three best" reviews of his latest novel and he does not read reviews online, saying: "A lot of mad people operate there."