The left-handed Dan (34-2), a Romania native, will try to hand Brook (33-0) his first loss.
Brook's promoter, Eddie Hearn, confirmed the fight plans at a news conference Thursday.
"I'm getting this out of the way," Brook said of the bout. "I know he wil be unbelievably hungry but he's in against me and I'm going to work twice as hard to hold onto it."
Brook, 28, will make his first defence of the title he won in a 12-round decision last August over Shawn Porter in Carson, Calif. Dan became the mandatory challenger with a split-decision win over Kevin Bizier on Dec. 19.
It was a second win in 13 months for Dan in Bizier's hometown of Quebec City. Dan's only losses were to Selcuk Aydin in Turkey in 2010 and 2011.
Brook is on the mend from stab wounds to both legs suffered during a night out while on vacation in Tenerife a few weeks after winning the IBF title.
A win over Dan could put Brook into some high-profile fights later this year, including a hoped-for showdown with fellow Brit Amir Khan.