These findings on one of the biggest energy projects on Canada's negotiating table come as Foreign Affairs Minister John Baird visits Washington D.C. in part to continue efforts to convince the Obama government to approve the pipeline.
The latest numbers from Nanos Research found that nearly 95 per cent of Canadians are aware of Keystone XL, but while just over half of Canadians still support the pipeline, that number is on the decline.
Fifteen per cent of Canadians had negative impressions of Keystone according to a poll conducted last April. By the time December rolled around, that number had jumped to 27 per cent. Meanwhile, positive or somewhat positive impressions had dropped from 60 to 47 per cent.
That decline was also evident when Canadians were asked further whether or not they support approval of the pipeline.
Canadians who would support or somewhat support the pipeline's approval dropped to 52 per cent by the end of the year from 68 per cent in April. When it came to opponents of the pipeline, Nanos Research found the number of Canadians who oppose the pipeline jumped 11 points, from to 24 per cent from 13.
"It has to be troublesome for proponents of the pipeline and also the prime minister, who's put his shoulder to the wheel to move this forward," said Nik Nanos, president and CEO of Nanos Research.
On CBC News Network's Power & Politics, Nanos told host Evan Solomon that the more debate there is over whether or not the pipeline should be approved, the more scrutiny it will face.
"The reality is that over time, it just looks like more of an imperfect pipeline."
Nanos also reasons that the Senate expense scandal has usurped the public narrative. As a result, he says, Keystone XL just hasn't had enough attention from the government.
The April poll numbers are based on random telephone (cellphone and landline) interviews with 1,013 Canadians between April 6 and 9. The December poll numbers used the same methodology with 1,000 Canadians between Dec. 14 and 16. The results are accurate to within 3.1 percentage points, 19 times out of 20.