Onex Corporation (TSX:ONEX) is exploring a sale of USI Insurance Services, LLC, hoping that a deal will value the U.S. insurance brokerage at as much as $4 billion, including debt, according to people familiar with the matter. Onex is working with Bank of America Corp on an auction for USI, the people said this week, cautioning that no deal is certain. The sources asked not to be identified because the sale process is confidential. USI and Onex did not respond to requests for comment, while Bank of America declined to comment.