connection_example.py

from google.cloud.sql.connector import Connector
import sqlalchemy

# wrap engine creation so arguments are dynamically passed
def init_connection_engine(connector: Connector, instance_connection_name: str, user: str, password: str):
    def getconn():
        connection = connector.connect(
            instance_connection_name,
            "pg8000",
            user=user,
            password=password,
            db="YOUR_DB",
        )
        return connection

    engine = sqlalchemy.create_engine(
        "postgresql+pg8000://",
        creator=getconn,
    )
    engine.dialect.description_encoding = None
    return engine

# your application code
def db_connect():
  with Connector() as connector:
    pool = init_connection_engine(connector, "project:region:instance1", "user1", "pass1")
    pool2 = init_connection_engine(connector, "project:region:instance1", "user2", "pass2")
    # ... connect to pools