TORONTO — Imax Corp. has signed a deal to sell three more giant-screen theater systems to Cinema Plus Ltd., following last year’s three-theater agreement with its Australian licensee.Toronto-based Imax said Wednesday that the three theaters in the new deal will add $10 million to its order back-log, which stood at $131.8 million at Dec. 31, 1996. Imax has focused expansion in the Pacific Rim region, which it says is underserved. Aussie success Since Cinema Plus opened its first Imax theater at Sydney’s Darling Harbour four months ago, 300,000 patrons have passed through the turnstiles. The second theater is scheduled to open in Melbourne in November. Tentative future sites include Auckland, Perth, Brisbane and Adelaide. Cinema Plus has an option for two addi-tional theaters. Cinema Plus also confirmed Wednesday that Brian Hall, currently Imax marketing vice president for Japan and the Asia-Pacific region, will become its new managing director. Hall, who was already a non-executive director of Cinema Plus, replaces Julie Steiner, who resigned under pressure from the directors, who made no secret of their plans to dump her. Imax said it will name a replacement for Hall in as little as a week.