Talks to have one of Belgium's regions lift a veto on the European Union's free trade deal with Canada continue on the day that the landmark agreement was supposed to be officially signed in Brussels.

The Belgian government and regional leaders continued Thursday to fine tune the wording of the agreement to address concerns including the impact on farming and corporate dispute settlements.

The EU presidency said that "the EU-Canada summit will not start today as planned" but left it open as to whether it might simply be delayed to later in the day.

But with Canadian Prime Minister Justin Trudeau having to travel to Brussels and approvals still pending from both the EU and Belgian regions, a summit on Thursday becomes more unlikely by the hour.