Hugh Jackman is the one that lands his voice to Bunnymund, and he's also the reason for Aster's Aussie accent. The authors didn't think to make him Australian at the beginning, but then Jackman pushed and added all the slang he could come up and voila, the perfect Bunnymund came out.
Hugh Jakman is an Australian actor, whose mostly known for Wolverine, but he has other lead roles that he's known for, for example Les Miserables, Real Steel, Van Helsing, Austrlia... and more.
He was born on 11th April 1968 in suburb of Melbourne, Austrlia. He started in TV shows as actor, and then went for the movies. He is able to act, sing and dance.
I personally think, he did an awesome job with giving Bunnymund his voice, he is a really good actor, and he gave a personality to the character, and made him something really lovable, aside, who doesn't swoon when Jackman says: "mate"