The new rules state that takeovers of Canadian firms in the oilsands by foreign state-owned enterprises will be approved only on an "exceptional basis."

"The limit is already set in place and that's the way they're going to handle future Chinese investments," Jiang said.

While the approval did not come as a shock to Jiang, the accompanying restrictions for future foreign investments did.

"It's just saying there will be no more overall large scale takeovers. and that's a little bit surprising," he said. "I had expected a lot of guidelines, but they basically said we're done with you in terms of big takeovers at the scale of Nexen."

But CEO of Asia Pacific Foundation of Canada Yuen Pau Woo has a different take on the situation. He believes the approval as well as new guidelines, are consistent with the government's advocacy of stronger economic relations with Asia and its emphasis on diversifying energy exports away from the United States.

"The deals were approved because they are good for Canada," he said.

Despite the accompanying restrictions for future foreign investments, Woo said the overall message is positive.

"Actions speak louder than words, and the approval of over $20-billion in foreign state-owned enterprise investment is more important than the qualifications that accompanied the announcement," he said.

With Canada still getting used to the idea that Asian countries are major sources of capital, Woo said the government's new stance is partly a reaction to public opinion.

With the CNOOC-Nexen deal, as well as the Malaysian-owned Petronas' $6-billion buyout of Progress Energy Resources approved on Friday, he said it will provide an opportunity for CNOOC and other state-owned enterprises to set a good example by demonstrating that they are commercially-oriented and good corporate citizens.

"The most important part about today's decision is that CNOOC and Petronas were deemed to provide 'net benefit' to Canada. If they can do it, so can other state-owned enterprises," he said.

Both analysts believe this is just the beginning of a long list of challenges for CNOOC. Having closed the deal in such public circumstances, the company will have a lot to prove in the coming years.

It's one thing to win the bid, but a whole other issue entirely on whether CNOOC has the capacity and the right combination of tools to make it all work, said Jiang.

"It is an unanswered question, I think it's a huge challenge," he said.