The European Union has given Belgium until late on Monday to overcome opposition to a free trade deal with Canada from its French-speaking region or a summit to sign the pact that could boost both economies is off, EU sources said on Sunday.

EU trade negotiators are rushing to assuage the Walloon government's concerns before the Monday deadline set by Canadian Prime Minister Justin Trudeau to decide whether to fly to Brussels, according sources familiar with the matter.

Canada says it is ready to sign the pact as planned on Thursday and year-long negotiations were over, with trade minister Chrystia Freeland saying "the ball is in the EU court."

All 28 EU governments support the Comprehensive Economic and Trade Agreement (CETA), but Belgium cannot give assent without backing from each of its regional administrations.

French-speaking Wallonia has steadfastly opposed it, saying the deal is bad for Europe's farmers and gives too much power to global corporate interests.

"It's disgusting the way this has [played] out," global markets analyst Patrick Young told CBC News. "Ultimately to be let down at the 11th hour, actually really at one minute before midnight before the signing of the deal, has been absolutely appalling."

In a last-ditch bid to secure Walloon backing, EU trade officials are offering tweaks to a political declaration appended to the treaty, an EU source said.

"Trade deals are win-win deals. Each party is able to build more stuff ,export more stuff and do more trade with the other country. And that's what's really, really frustrating," Young said.

'We are refused a few weeks'

Many EU leaders suspect the local government in Namur is using its devolved powers to play domestic politics. "This is first of all an inner-Belgian matter," an EU source said.

Walloon Socialist Party leader Elio Di Rupo, one of the most vocal opponents of the deal, cast doubt an agreement could be reached next week.

"They took years to negotiate #CETA and we are refused a few weeks," Di Rupo, a former Belgian prime minister, tweeted on Sunday. "Will we reach a solution? All depends on the contents. If it doesn't change enough, we will maintain our opposition."

Wallonia's government head Paul Magnette, left, and European Parliament President Martin Schulz address the media on Saturday after their meeting regarding CETA (EU-Canada Comprehensive Economic and Trade Agreement) at the European Parliament in Brussels. (Nicolas Maeterlinck/AFP/Getty Images)

European Council President Donald Tusk, who chairs the collective body of the EU's leaders, will speak to Belgian Prime Minister Charles Michel by late on Monday, EU sources said, before informing Trudeau's government of the state of play.

"If Michel says he is not in a position to confirm that Belgium will be able to sign on Thursday, then we won't have the summit," a source said.

If postponed, no new summit date will be set, although the source said neither the EU nor Canada is willing to give up on a free trade pact that has been years in the making.

The issue is greater than just a trade deal with Canada, the EU's 12th-largest trading partner.

If CETA fails, the EU's hopes of completing similar deals with the United States or Japan would be in tatters, undermining a bloc already battered by Britain's vote to leave and disputes over Europe's migration crisis.

"The Eurozone still has the fundamental problems that we've talked about for years," Young said. "It's really a disaster, and that's why people are very, very annoyed, upset and frustrated because it feels like the European Union is being held for ransom by one small, not very important region out of 28 nations."