As some have said you can either get loans and use mercs to beat down France alone with more troops or you can restart until Burgundy, Aragon or castile (or 2-3 of them if you can) are friendly with you and rivalled to France or want their land so you can ally them and call them into the war promising land and giving them nothing. Make sure to improve relations with any nations that may join a coalition while at war and make sure you don't finish the war with France until after the war of the roses event has fired. When this event starts you get a new ruler and will lose the PU if you peace out before it.
Some players will now conquer France as England (rather than forcing the PU) due to enforcing PU's giving higher AE now, but you can still force PU them as long as you improve relations with nations that would join a coalition.
This is a older guide on YouTube from 2 years ago and will still work to win the war now. He allies and calls in Castile with a promise of land as a distraction while using mercs so that the enemy spends its time sieging down your ally while you siege down France. Just remember to improve relations to avoid a coalition forming as its more AE now than 2 years ago.
Edit. Even better when you are friendly with Burgundy and can ally them to get the Burgundy Inheritance also
