Fascinating thread.
Though touched on here and there, I would expect that the Navy (U.S. & Canada) would have had a far more dominate role much in the same way that it was used and dominated events in the Pacific. Probably the only facet of the Pacific that would not be replicated in the Atlantic to the same extent would be submarine warfare as Europe and surrounding areas would be far more able to supply itself vs. Japan needing just about everything shipped in - literally.
As for the USAAC, I'd estimate that Greenland and more so, Iceland, would have had a more important role as flying direct from ConUS would have not been possible or too costly due to attrition. A developed XB-19 followed by B-29s and B-32s followed up by the B-36 and B-35/B-49s for long range bombing with Navy fighter escorts.
Invasion route would have been Canada to Greenland to Iceland on to Ireland or Scotland and then on into Great Britain. Using Google Earth to eye things, the Faroe and Orkney Islands are not large enough to build up and stockpile enough to make a D-Day size invasion leap from Iceland to Great Britain but probably would make for decent landbased "carriers" for fighter and anti-submarine cover.
There's a fascinating Sci-Fi book written by James P. Hogan called "The Proteus Operation" that touches on some of the 'what-ifs" - take a look at:
http://www.jamesphogan.com/books/info.p ... md=summary
Enjoy the Day! Mark