Strain joined Sun Life in 2002 when it acquired smaller peer Clarica. He has been chief financial officer since June 2017.

Prior to his current role, he was president of the insurer's operations in Asia, experience that will come in handy as the company continues to explore options to expand its presence in the region.

The insurer is also seeking to add to its group benefits and stop-loss businesses in the United States.

As CEO, Strain will continue on the path Sun Life is already on, expanding its digital capabilities and increasing its focus on sustainability, he told Reuters.

"I've worked really closely with Dean and the executive team on strategy," Strain said in an interview. "I'm going to continue to build on this strategy."

Strain will remain chief financial officer until a replacement is appointed in the first half of 2021, Sun Life said in a statement.

"We believe Mr. Strain will be a suitable replacement as he has a strong track record in business transformation and as a finance executive," Canaccord Genuity analyst Scott Chan said in a note.

Connor, who was previously head of Sun Life's Canadian operations and chief operating officer, will also retire from Sun Life's board of directors, which Strain will join, the company said.

"I will be turning 65 a couple of months after retiring," Connor told Reuters. "It was my intent to retire around this age and think about the next chapter."

Sun Life shares were flat on Wednesday afternoon at C$57.08 in Toronto, versus a 0.3% increase in the Toronto stock benchmark.

(Reporting by Sohini Podder and Noor Zainab Hussain in Bengaluru and Nichola Saminather in Toronto; Editing by Chris Reese and Matthew Lewis)