The Canadian government is backing New Zealand's bid for a temporary seat on the UN Security Council, throwing its support behind a long-time ally that's promising a stronger voice for less-influential countries if it's elected.

Ottawa lost its own bid for a Security Council seat in 2010, an embarrassing defeat that was followed by several years of cool relations between Prime Minister Stephen Harper and the multilateral body. New Zealand is vying this year for one of two seats set to open up in the Western Europe and Other category, but faces stiff competition in rivals Turkey and Spain.

A spokesperson for the Department of Foreign Affairs said the government would not disclose its voting intentions because the election takes place by secret ballot. But a source familiar with the New Zealand campaign said Canada is supportive of that country's bid, and internal records show Ottawa was prepared to dispense advice and advocate on New Zealand's behalf.

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China, France, Russia, Britain and the United States have permanent status on the 15-member Security Council and the power to veto proposed resolutions, and the remaining seats are filled through regular elections, with each member serving a two-year term. A total of five temporary seats are on the line in this year's election, which is scheduled for Oct. 16.

Three of those seats should be decided easily: Angola, Venezuela and Malaysia are all running unopposed in their regional groups. The remaining two, which are reserved for countries in the UN's Western European and Other grouping, are being contested by Spain, Turkey and New Zealand.

Colin Robertson, a former Canadian envoy to Washington, said New Zealand enters the race at a disadvantage, particularly compared with Spain, which can expect the support of other European Union members who tend to vote as a group. Turkey may also have an advantage in the election as an influential country with a growing role in global security issues.

"New Zealand is hoping to win just on merit," Mr. Robertson said, noting the country has long been an active and steadfast supporter of the UN. "But it's uphill for them compared with Spain or Turkey."

A booklet on New Zealand's candidacy emphasizes a commitment to multilateralism and the government's interest in bringing the voices of smaller states to the Security Council table. Last week, New Zealand's Foreign Minister told The Wall Street Journal that, if elected, his government's priorities would include containing Islamic State militants and finding a solution to the crisis in Ukraine.

Internal records obtained through Access to Information laws show the Canadian government expressed support for New Zealand's bid and may have lobbied Caribbean countries on New Zealand's behalf. "Canada is actively supporting New Zealand's bid for election to the United Nations Security Council for 2015-16, particularly among Caribbean nations," says a memo for the Prime Minister, dated April 12, 2013.

A second document, prepared for a meeting between Public Safety Minister Steven Blaney and then-New Zealand justice minister Judith Collins in July, 2013, said Canada supports New Zealand's bid and "is happy to share lessons learned from our previous campaign for a [UN Security Council] seat."

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A source familiar with New Zealand's campaign confirmed Canada has offered advice and support. There were "plenty of conversations" between officials from both countries over the course of New Zealand's bid, the source said, including talks about that country's candidacy and its efforts to secure votes. New Zealand has also discussed its candidacy with a number of other countries, the source said.

Adam Chapnick, a foreign policy expert at the Canadian Forces College in Toronto, said Canada, Australia and New Zealand have a long-standing, unwritten agreement to back each others' candidacies at the Security Council, in part because all three are outsiders in the Western European and Others regional grouping. The countries are also long-standing allies and are part of an intelligence-sharing relationship along with Britain and the United States.

Mr. Robertson added that he thinks the Canadian government was unfairly criticized for losing its 2010 bid, because it was already at a disadvantage as a non-EU candidate in a regional grouping dominated by Western European countries. There were other "mitigating" circumstances, he said, but "it's always going to be tough for Canada to get in because we work in a bloc that works to our disadvantage. And this holds true for the New Zealanders and Australia as well."