Environmentalists are wary of a deal announced yesterday in which U.S.-based Weyerhaeuser will pay nearly $2.5 billion in stock for Canada’s MacMillan Bloedel, merging two major North American timber and paper companies. MacMillan Bloedel has been at the center of many environmental conflicts over old-growth logging in British Columbia. Last year, the company announced that it would phase out clear-cutting and seek international environmental certification for its operations. Weyerhaeuser chief executive Steven Rogel declined to say yesterday whether Weyerhaeuser would uphold MacMillan Bloedel’s commitment to end clear-cutting in coastal forests within five years. The deal still needs approval from MacMillan Bloedel stockholders and U.S. and Canadian regulators.