However, consider the merchant class which dealt in finding goods abroad and shipping them back to Europe. Of course they would have both the motivation and the means to come to eastern North America, if they thought there was a profit in it. And the stuff they wanted was here: whales, cod, walrus, and lots and lots of timber.
It is entirely credible that they would have set up expeditions to Newfoundland, Labrador and possibly farther inland. BUT NOT TOLD THE WHOLE WORLD WHERE THEY WERE GETTING THEIR GOODS for obvious reasons. They didn't want the competition here. Logically they might have set up at least seasonal, and possibly semi-permanent settlements to organize their resource-harvesting activities
I like this concept, but am still doubtful that such information could have been kept secret. Human nature would seem to dictate that members of a crew who conquered the Atlantic, encountered unknown tribes of peoples, and saw all sorts of plants, animals, and geography that were unknown in their world, would have talked. I am unaware of any pre-Columbian writings in any European culture which speak of this new land, other than the Viking Sagas. Since the Viking settlement occurred ca 1000 AD, why, if the knowledge was widespread, was there not a subsequent rush to colonization? True, European ocean craft of the era was very primitive compared to 500 years later, and this could go a long way toward explaining it. But if there was specific record of this Vinland discovery, I would be highly interested in seeing it, and would be even more interested to know if such writings led Columbus to believe that in fact there was a new land between Europe and India.