OTTAWA - Democrat Barack Obama would crush Republican John McCain in the U.S. presidential race by an almost four-to-one margin -- 56 per cent to 15 -- if it were up to Canadians.

That's the conclusion of a new Canadian Press-Harris-Decima poll that, for the first time, gauges Canadian opinion on a head-to-head contest between the Republican candidate and the presumptive Democratic nominee.

The same survey suggests Canadians consider the current occupant of the White House, George W. Bush, among the worst presidents ever -- if not the worst.

Forty-two per cent of respondents called Bush one of the worst presidents in U.S. history, 23 per cent said he was the absolute worst.

Only four per cent said he was among the better ones, and less than one per cent called Bush the best ever.

Pollster Bruce Anderson says the survey results are surprising even in a country that traditionally favours Democrats.

"While Canadians generally tilt more towards the Democratic Party than the Republican Party, this degree of disaffection is quite remarkable,'' said the head of Harris-Decima.

"It cuts across the political spectrum. Very few Conservatives in Canada are prepared to say they have been satisfied, let alone enthusiastic about the accomplishments of Mr. Bush.''

While some of that antipathy toward the incumbent Republican could explain Canadians' overwhelming support for the presumed Democratic nominee, Anderson says Canadians like Obama for other reasons.

He says the candidate's three main promises are in lock-step with Canadian public opinion. His public declarations that he would renegotiate NAFTA appear, so far, to have ruffled few Canadian feathers.

Obama has said his first priorities in office would be expanding public health care, ending the war in Iraq, and creating an integrated environmental-energy policy.

"They're pretty consistent with Canadian values,'' Anderson said.

The results were similar among different age groups, gender's, income categories, and in every province.

Even in the province where Obama was least popular -- Alberta -- respondents favoured him by a 28-point margin over McCain. Fifty-one per cent of respondents there supported Obama, and 23 per cent preferred McCain.

Obama was most popular in Quebec where 61 per cent of respondents favoured him, and was almost equally popular in Manitoba, Saskatchewan, and British Columbia.

While the Illinois senator has struggled somewhat with lower-income and female voters in his primary contests against Hillary Clinton, the survey suggests he would not have no problem with them in Canada.

He received statistically identical support levels from men and women, and from respondents in different income categories.

The survey of 1,000 Canadians was conducted May 15-18 and is considered accurate to within 3.1 percentage points, 19 times in 20.