Saying "it's hard to pick just one," Opposition House leader Ralph Goodale threw his support behind federal Liberal leadership candidate Bob Rae on Tuesday, one day before the convention to select a new leader begins.

Goodale, Liberal MP for the Regina-area riding of Wascana, said Rae is the candidate most capable of promoting Canadian unity, the most "skilled at statecraft" and the best person to replace Stephen Harper as prime minister. Rae is former premier of Ontario.

Bob Rae, left, with Ralph Goodale in Ottawa on Tuesday.
(CBC)

"This is a difficult choice," Goodale said. "We have many strong candidates and they are all friends of mine. But at the end of the day, you either sit on the sidelines and be a spectator, or you enter the fray. On balance, I thought Bob Rae is the best positioned to take on Mr. Harper."

Goodale said the Harper government is doing "neo-conservative" damage to Canada, saying it is mean and vindictive, and Rae is the best person to counter the Conservatives with their "Republican" values.

"The Harper regime is the most rigidly ideological government in the history of Canada. Its economic and social politics are focused exclusively on a narrow and extreme base," he said.

"We need a Canada that is bigger than that, more inclusive and fair, more ambitious, more hopeful, more visionary. I believe Bob Rae and the Liberal party can offer that better alternative. We must give Canadians something to vote for, not just against."

Goodale, who was finance minister in the Paul Martin government, said he believes in fiscal responsibility and a sense of national purpose, and Rae offers both. "He has huge experience in all dimensions of public life," he said.

The Liberal leadership convention opens Wednesday in Montreal, with registration scheduled to take place on Tuesday, but delegates are not expected to vote on a new leader until Saturday. About 5,000 delegates are expected to attend.

There are eight leadership candidates in all, but the four expected to have the best shot at the top Liberal job are Rae, Toronto MP Michael Ignatieff, former Ontario cabinet minister Gerard Kennedy and former federal minister Stéphane Dion.