CHINA'S CNOOC Ltd's successful acquisition of Nexen Inc may spur more foreign takeovers in North America's energy sector although Canada signalled it would tighten investment rules.

Canada approved CNOOC's US$15.1 billion bid for Nexen, China's largest ever foreign takeover, and also Malaysian state firm Petronas' purchase of Progress Energy Resources Corp over the weekend.

But Prime Minister Stephen Harper called the approvals "the end of a trend" as he signalled Canada would not allow a foreign government to control the nation's oil sands.

Still analysts are certain Canada will not completely close the door to beneficial foreign investments.

"We believe the government officials' statements were made to appease the many politicians who had voiced concerns recently about the CNOOC and Petronas deals," said Mirae Asset analyst Gordon Kwan.

He said the successful deals may see more foreign takeover proposals for North American assets.

The CNOOC/Nexen deal will still need approval from US regulators as 8 percent of Nexen's output comes from the US, but analysts are confident the US will not block the deal.