Just to extrapolate on idea, while still considering it risky and thus unhistoric, there's the issue of aircraft strength.
According to Wiki, total Luftwaffe day fighter strength on 31 May 1944 was 1063 and bomber strength 841. The Luftwaffe total day fighter strength could be more than well be exceeded by RN/USN carrier air if deemed necessary. RN big decks available alone could operate hundreds of aircraft, add the USN's Atlantic large carrier Ranger and a number of escort carriers and necessary air strength is there. RN escort carrier strength alone also was more than required for both ASW and significant landing support. By 1944 RN had 34 Bogue-class CVE's alone, each with capability of some 20 fighters in open ocean conditions.
And this is not counting the long range planes which could be operated from UK bases and the fact that Luftwaffe could not withdraw all it's units from Eastern Front and Mediterranean. Allied medium bombers could well operate from UK bases. One should also not forget the Allied qualitative superiority at this point of war.
Thus, Allied air would dominate even in case of a North Sea landing and this would not even require substantial withdrawals from the Pacific theater. However, the aerial domination would not be as substantial as in Normandy landings and this would entail perhaps larger convoy losses if largest part of the Allied Atlantic CVE strength was used to support landings. On the other hand, Allies could well survive much more severe convoy losses.
Second question is what forces could be landed and sustained? As for the airborne troops, the range of aircraft would be enough for landings in North Sea coast of Germany or Denmark. Thus, the historical three airborne divisions could be sent.
As for the ground troops, the size of the initial assault would be roughly similar to historical strength. However, the following build-up would be slower due to larger distances. As for the initial assault, the conditions are more difficult than in the Overlord, but the defenses are much weaker. There are also several not-so-well defended harbors which can add to logistical strength of the Allied force.