A second amphibious landing into the Scheldt marshes looks difficult to stage, because of limited availability of troops. The landing craft and ships are also needed to carry supplies to the Normandy beaches.
The Germans are currently (20-24th July) putting all their available forces into trying to crush the Normandy bridgehead, but it isn't working. It seems likely that when their line cracks, they won't have much available to oppose an advance to the River Seine and beyond. The Fuller-Knight document is consistent with this.
The plan is that the troops advancing up the Channel coast (expected to be Canadian First Army, opposing German 15th Army) should take any ports that can be seized quickly. Since it's expected that the Germans will fort up in as many of them as they can, they should be contained there and left to rot. Antwerp has more capacity than all of those ports put together, and is well placed for an advance into Germany. Having the use of it would allow supplying all the Allied armies, so it's the primary target.
There needs to be some degree of obfuscation in the troop movements, depending on the speed of the advance. We don't want to make it too obvious that we're mainly interested in Antwerp; the Free French would complain, and the Germans might manage to do something about it.
Since Antwerp is only usable if the Allies hold both banks of the Scheldt, it's important to have as many of the Canadians as possible available to take the river's south bank quickly, before the Germans get organised.
Whoever takes Antwerp itself needs to press on across the Dutch border, and take the narrow base of the South Beveland peninsula, which carries a railway line. That cuts off the retreat and supplies of the German troops in South Beveland and the fortified island of Walcheren. Once more troops have been brought up, those areas should be taken as rapidly as possible, along with a buffer zone to prevent German counter-attacks reaching Antwerp.
The Germans may well try to evacuate troops by boat across the Scheldt to Walcheren or South Beveland. They may also try to evacuate troops further north across the Oosterschelde inlet to the Dutch islands of Schouwen-Duiveland and Tholen.
The 2nd Tactical Air Force should be able to impede evacuations by water during the day, but they can't operate at night. The best countermeasure to German night crossings is RAF Coastal Command's anti-shipping aircraft, which have ASV radar, cannon, rockets, and torpedoes. Use of Window should limit the effectiveness of German Flack.