The prime minister will be accompanied by his foreign affairs and trade ministers, as well as a delegation of business executives.
Harper will also discuss illegal human smuggling with Thailand's Prime Minister Yingluck Shinawatra. Thailand was a staging point for migrant ships bringing Tamil asylum seekers to Canada in recent years.
On March 25-26, Harper will make his third visit to Japan, Canada's fifth largest trading partner.
"We are interested in boosting trade, particularly in the Asia-Pacific region. That's why we're going on this trip on the heels of a China trip," said Harper's spokesman Andrew MacDougall.
Harper visited China last month.
In South Korea on March 26-27, Harper will join leaders of 53 other nations for a nuclear security summit.
Topping the agenda will be the problems of securing loose nuclear material and dealing with "rogue nations such as Iran and North Korea," MacDougall said.