It was due to a cracked windshield and pressurization issues. Following from Transport Canada daily occurrence reports.
AFR085, a Boeing 777-200 operated by Air France, was en route IFR from San Francisco (KSFO) to Paris-Charles de Gaulle (LFPG). At 0630Z in the vicinity of 63N/80W, the crew declared an emergency due to a pressurization problem resulting from a crack in the windscreen. The aircraft descended to an altitude of 10,000 feet in order to stabilize the situation and requested to divert to Montréal/Trudeau (CYUL). Shortly thereafter the crew cancelled the emergency but continued to Montréal/Trudeau. The aircraft landed without incident at 0929Z. No impact on ATC operations.
[Edited 2012-07-03 19:57:25]