A publisher can signal its preferred URL, but a search engine makes its own selection. The canonical annotation does not redirect readers or stop another URL from loading. (Google canonical URL documentation ↗)
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Keeping one article address
Illustrative duplicate-URL case: the same article is available at /budget-vote/ and /budget-vote/?newsletter=email. The publisher signals /budget-vote/ as the preferred article URL and has section pages link to it. Those section listing pages are not duplicate copies of the article.
A canonical signal is not a redirect
Section pages that list an article are separate pages, not duplicate copies of its full text. Keep their own page identities. When checking a duplicate article, distinguish the canonical URL you declared from the one Google actually selected.
What to inspect after a URL change
Open the old and preferred addresses separately. Record the response, the stated preferred address and which one appears in navigation. If those point in different directions, give the developer the actual URL pair so the repair can address the conflicting signals. Save the expected destination with the change request before updating templates.