3 points, but forget goal difference - that ship has sailed.
For GD to have any relevance, we have to finish level on points with City, and that would most likely happen if we both go on to match each other's results with the exception of them beating us.
Even if we only lost 1-0, that's an extra goal for them and +2 to their GD vs us.
That's a GD of +7 which means we'd have to win every game by one more goal than City win theirs, or have some really massive blowout wins and City just keep doing 1-0. It's not impossible, just highly improbable.