The Utah Jazz have made it clear that they do not want to retain Boozer beyond his current contract.
With Portland offering Millsap a new contract they need to clear cap space to match.
Sign and trade Wally for Boozer, Wally's contract should be only partially guaranteed so that the Jazz can buy him out if they want to. However, the contact amount has to match trade regulations (approximately $10.2 mill). The advantage for Utah is that they can retain Millsap and the advantage for Cleveland is that they get Boozer, a scoring and rebounding PF. For Boozer - he plays on a team that can win it all next season and Wally, if bought out, can seek further employment.