Prime Minister Justin Trudeau’s government will provide low-cost leases of public land to developers and push factory construction of houses as a part of what it calls a “historic” plan to alleviate Canada’s housing disaster. A generation ago, the buyer’s agent had all the data — comparable neighborhood sales costs, tax histories, faculty district placement and particulars of the house — and was alleged to act as a comprehensive counselor. The case hinged on the commissions, normally of 6%, that sellers pay their brokers, who then cut up them with the buyers’ brokers. It has been a cornerstone of how …