Day 1:
Recruit one cavalry mercenary and infantry mercenary to force limit (I debase once and put burger influence to 75 and ask them for money). Ally Savoy, Aragon, Burgundy, whoever you can that France might ally (esp. Aragon). Do not rival anyone or the mission to force union will not show up. Ferry your armies to Normandy.
Day 30:
Declare on France and call in allies on promise of land (in my attempt only Burgundy would answer the call). Attack the stack in Paris with your entire army.
Sadly, Aragon hadn't rivalled France so they were allied in this war, but fortunately Burgundy was my ally. Overall, we had more troops than the enemy and although Burgundy peaced out midway through the war, I was able to snipe smaller sieging stacks by positioning armies to spread the enemy's forces thin.
I got a heir with strong claim during the war so I peaced out as soon as I was able. Changing monarchs due to events will break the union if your subject is not loyal, so beware accepting new regents/the War of Roses before peace out France. Anyway, I took one loan all in all, depleted all my manpower, and this wasn't even a particularly good run (due to France-Aragon alliance). Sometimes, you will struggle due to unlucky combat rolls if France consolidates their troops and attack you when you're sieging Paris, but it's such an easy start to get going that it's never an issue if you have to restart during/after the war.
Priority #1 after the war is to get French liberty desire below 50%. Priority #2 for me is to contain Iberia from forming colonies, so expansion into the peninsula is mandatory. Meanwhile I consolidate my hold on the Isles and turn my gaze eastwards to the Kalmar Union, the Commonwealth, and the lands of the Rus. The Baltic node must be controlled by the English so the ducats may flow.