Have COPR and will be landing in July 2025. I will not be working in Canada, (retiring).
As a resident, in my tax return for 2025, will I have to declare and pay tax on earnings outside of Canada before arrival (January to June 2025)?
Pull out the tax return and package for new permanent residents from the CRA website, it lays out the methodologies for various aspects. You can also look at tax return from most recent year available (i.e. 2023, 2024 ones will be out soonish) to see how it's actually done (online websites too if you want to plug in numbers to understand).
https://www.canada.ca/en/revenue-agency/services/tax/international-non-residents/individuals-leaving-entering-canada-non-residents/newcomers-canada-immigrants.html
[Obviously the details can change each year but the overall approach doesn't usually that much.]
In rather simple terms: your earnings outside Canada before arrival won't be taxed, but you'll need to report them. They will affect some benefits etc that you may be eligible for.
You'll also need to report assets outside Canada - mainly a value and where they are, which will affect future earnings (cap gains for example) when you dispose of them.
For Canadian residents, Canada taxes foreign income (eg if you get retirement income from abroad, you'll pay taxes on it). BUT: taxes paid abroad will usually be deducted from amounts you would have to pay. Specifics of which country etc can matter because of dual taxation treaties. So if taxes in Canada are higher than what youv'e paid abroad, you may have some owing on the difference.
This overview is NOT advice, you may be best to get a tax person to help.