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.
Theresa May has pressed the EU for a "bespoke" Brexit deal that would allow the UK to control migration while still keeping strong trade links, a spokeman has said.
The prime minister vowed to carry out talks in a "positive and constructive spirit" in a one-on-one meeting with European Commission president Jean-Claude Juncker in Brussels.
It came after she was sidelined at a summit which saw her only allowed to address fellow leaders briefly on the UK's plans for Brexit.
A No 10 spokesman said Mrs May had stressed that Britain would remain a strong partner to Europe even after leaving the bloc, as she tries to set a positive tone on the difficult talks.
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.