North American lumber prices are poised to return to highs last seen in June after heavy rains and flooding in Canada's westernmost province closed roads and caused the world's biggest producer to curb shipments.  Lumber futures rose as much as 3.8% in Chicago on Tuesday to $824.50 per 1,000 board feet, on pace for the highest settlement price since June 24, according to data compiled by Bloomberg. Prices have climbed for the past two days, extending gains after West Fraser Timber Co. Ltd. said its western Canadian lumber weekly shipments plunged ...