An Air Canada Embraer ERJ-190, registration C-FHNV performing flight AC-668 from Montreal,QC to Halifax,NS (Canada) with 103 people on board, was in the initial climb out of Montreal when the crew reported smoke in the cockpit, stopped the climb at about 4000 feet and returned to Montreal for a safe landing about 9 minutes after departure. The Canadian TSB following a lavatory smoke indication the crew reported smoke in the cockpit, requested emergency services on stand by and returned to Montreal. Maintenance found burnt debris in an air duct off the right hand engine (CF34). The right hand engine had been replaced and the aircraft was on its first flight since.