US President Donald Trump is barring appointments to the WTO's Appellate Body, saying its judges have overstepped their mandate and ignored their instructions.

Unless the block is lifted, the world's top trade court will be unable to hear appeals in international trade disputes by December.

Trudeau, speaking after a meeting with top EU officials in Montreal, said Canada backed existing attempts to restore a fully operational Appellate Body.

"In the event that those efforts are unsuccessful, we need to be prepared. So we have been working with the European Union to find an interim fix," he told a news conference.

"After this summit we are closer to finalizing an agreement which would help preserve the function of an appeal system within the WTO until we find a more permanent solution."

A joint statement issued after the Montreal meeting said the fix involved setting up an interim appeal arbitration arrangement based on existing WTO rules.

The EU last month proposed using WTO arbitration rules to set up a shadow version of the body and keep the appeals process moving, but there is uncertainty about how such a structure would work.

Cecilia Malmstrom, the EU's trade chief, told the news conference that the deal on a possible fix "sends a strong message of our shared objective to ensure the full effectiveness of the WTO and the stability of world trade."