Cnooc's bid is the first super-big buy into NorthAm energy (three times the Syncrude buy in 2010). It follows similar buys into Australia (Rio Tinto), Iraq-KRG (Addax) and Latam (Repsol Brazil).
Cnooc, by all accounts, learned from the failed Unocal bid and built all manner of business and personal networks before launching this bid. Lotsa regulatory hurdles on this one, but I'm betting Canada ultimately says yes, especially since Nexen's board backs it. Ottawa can't close itself off to China's resource demand and opening itself up to that flow requires some buy-back transactions like this.