It is not that unfeasible to have a Scandinavian presence in North America in the late middle ages. A few decades before the Kalmar Union, Sweden and Norway had the same king, and reports came that the western settlement of Greenland had left and joined the pagans beyond the western sea.
Suppose that there had been greater communications with the central power, and that this migration had been actively supported by the king, sending some troops and additional colonists. If this occurs around 1340, a decade or so before the plague, we might find a fair number of people who are willing to try out an unknown land.
This first wave founds some villages, and since the crown makes sure of continuous communications and supervision, there is a steady trickle of newcomers every year, so additional villages and even towns are built. By 1500, they, optimistically, could have taken the whole of Newfoundland, but that is a large area, and they are still few.
In the age of explorations, 1500-1700, they do have an advantage to other European powers, since they already have a foothold, know the lay of the land, and are close to their bases, so the final result might be that approximately Canada is Scandinavian, while the US area is taken by others.