In 2011, Beijing-based Sinopec (China Petroleum and Chemical Corp) bought Calgary-based Daylight Energy Ltd for $2.2 billion. Last year, PetroChina became the first Chinese State-owned firm to wholly own Calgary-based Athabasca Oil Sands Corp for $674 million.

Recently, Sunshine Oilsands Ltd signed an agreement with China Oilfield Services Ltd for cooperation in developing multiple thermal fluid oil-sands exploration technology in Canada.

John Zahary, president and CEO of Calgary-based Sunshine Oilsands, the first Canadian oil-sands listing on the Hong Kong Stock Exchange, said while the CNOOC acquisition of Nexen is big, "it hasn't completely changed things".

"A significant majority of Nexen's assets are outside Canada despite the fact that Nexen is headquartered in Canada," he said. "Thus, the deal doesn't even have as much impact on Canadian oil industry as some smaller deals where the assets are in Canada."

From his office window, Zahary can see Nexen headquarters. After some recent exchanges with CNOOC executives at a local event, he described his new neighbor as "very friendly and eager to be part of the community".

Most of the Chinese investment has come from State-owned enterprises into Canada's natural resource projects, and it has drawn scrutiny and criticism from members of the governing Conservative Party and local environmentalists.

The CNOOC-Nexen deal took about five months for the government of Prime Minister Stephen Harper to review before approving it in December. While recognizing the importance of foreign investment in the country's economy, Harper described the decision as "not the beginning of a trend, but rather the end of a trend".

Some see the deal as a boost for Sino-Canada economic ties.