Prime Minister Theresa May has said Britain will play a "full and active role in the EU" until it leaves.
Following Brexit, Britain will remain "open" and "outward looking" and is committed to trading freely with other European countries, she said.
The prime minister is attending her first EU summit following the referendum.
Canada's free trade deal could be the last for the EU, the bloc's President Donald Tusk said.
The CETA deal with Canada is being delayed after one regional parliament in Belgium vetoed it and voiced concerns over some its terms.
Arriving for the summit, which the prime minister is also attending, Tusk said Brexit will not be discussed.
Trade will be a major issue at the two-day EU summit in Brussels, which begins today.
Tusk warned the CETA deal risked being the last such accord for the bloc unless it improves its trade policies.
Asked if she was undermining the UK position, she said: "You can't undermine something that doesn't exist."
The deal would set up a free trade zone between the EU and Canada - and could be an important test for the UK's Brexit negotiations.
European Commission President said an EU-Canada free trade deal would help end Canadian visa restrictions for Romanians and Bulgarians.