One alternative way to get more settlers in Norse Greenland in the fairly warm early C11th, and then either a useful timber/ fur-trade base in Nova Scotia/ Labrador/ the St. Lawrence valley a little later, is to up the ante on current politico-military crises in Norway. That could push targeted and ship-owning landowner rivals of the warlord that comes out on top in Norway heading off to Iceland , then Greenland, looking for a safe new land to settle and exploit, and taking their dependants along with them - as in the late C9th and early C10th the (written down later and probably exaggerating) sagas say that the establishment of a strong new centralised kingship by Harald 'Finehair' c. 870 to 920 led to his rivals having to flee abroad and settle elsewhere. They mostly ended up in the then fairly empty Shetlands and Orkneys, with the emergence of a new Jarldom in the latter following - and Harald having to go there himself later with a fleet to neutralise the threat of invasion from there by his vengeful exiled enemies.
If we get a similar crisis in Norway after the discovery of 'Vinland' and the first expeditions there, any defeated nobles who fled to Greenland might well decide as fertile land was in short supply there not to challenge the existing settlers there but to risk a move to new lands in N America. If they had sufficient numbers of warriors and adequate weaponry - a few hundred well-armed men plus dependants - they could also risk taking on the local 'Skraelings' (Athabascan Native Americans), who the first - and small groups of - Viking explorers would have reported to be poorly armed and lacking large bodies of disciplined warriors used to fighting pitched battles. A Scandinavian presence by a few hundred people, later expanding, in a fortified and defensible position by a bay in Nova Scotia or Cape Breton Island , or a headland overlooking the St Lawrence (the Quebec hilltop?), is plausible if the incoming numbers are sufficient and they know they have nothing to loose risking staying to explore, trade furs, and fight - eg if the main settlers in Greenland do not want them as potential rivals for scarce land or looters of their sheep herds (G mainly being pastoral not arable even in an optimum pre-Little Ice Age climate). Then the settlements would slowly expand, perhaps by intermarriage with some smaller local tribes who seek their valuable aid against aggressive rivals in a dispute over hunting-territory or who are sold Viking weapons in return for access on a regular basis to furs and timber to export to Greenland (short of trees to use to build houses) and Iceland. I can see the Scandinavians taking over a smallish and defensible offshore island off the Canadian Maritime Provinces which has useful timber and arable land resources resembling what they were used to in Norway , eg Prince Edward Island, as a reasonably plausible outcome - and if it was fairly far South it could survive when Greenland became difficult, with Greenlanders moving there too. From there, regular trading trips could follow down the coast to Cape Cod and the Hudson River within a few decades - and a settlement on an offshore position free from attack (Nantucket??) for trade and fishing in due course.
The likeliest crisis in Norway to encourage an exodus of defeated foes of a powerful new ruler - if the non-Norwegian intruder , Cnut of Denmark/ England (ruled in person or by proxy 1028-35) , is able to reverse his son and nominee King Swein's eviction in 1034/5 rather than dying , aged only around 40-45, in November 1035. (He died at Shaftesbury in Dorset; his son Swein's mother was Cnut's first wife or mistress, Aelfgifu of Northampton, a Midlands English 'Danelaw' woman), and S's full brother Harold 'Harefoot' succeeded Cnut in England in 1036-40. If Cnut has the health and energy to take Norway back from the new king, Magnus, in 1036 or 1037, using the resources of England and Denmark, then his putting down resistance by a purge of Magnus' supporters - he carried out a real life purge of the Anglo-Saxon leadership when he took over England in 1016-17, and was also known for mutilating hostages and trying to have rival princes murdered - is logical. Then there could be a large-scale flight of Magnus' supporters from Norway - and possibly when M's uncle Harald Hardradi leaves Byzantine employ in 1042 with his warriors he could decide to go off to Canada too. The Niagara Falls would not stop Viking explorers - they were used to carrying ships round rapids/ waterfalls on rivers from the Dnieper in Ukraine.
