https://www.psycopg.org/psycopg3/

On initial glance, it looks like we don't use anything that has changed in psycopg3.

https://www.psycopg.org/psycopg3/docs/basic/from_pg2.html

So this might be as simple as import psycopg3 in a try block with fallback to psycopg2.
Then setting up a CI to require psycopg3. Then running the test suite.

Will need to have some test/output that indicates the version 3 is running though
in case the CI environment has psycopg3 in it already.