Brookfield Asset Management Inc. and Onex Corp. are preparing an offer for IWG Plc that will value the commercial real estate company at about 2.7 billion pounds ($3.7 billion), people familiar with the matter said. Zug, Switzerland-based IWG, which owns office space and competes with New York-based WeWork Cos., said last month it had received an “indicative proposal” for a cash deal from the consortium. The group is lining up a firm offer of about 300 pence a share but not more than that, said the people, who asked not to be identified because the matter is private.