I think I'm going to go the opposite direction and make France even weaker. Flanders, Normandy, and Britanny will probably fall into the British cultural/political sphere, if possible.
Look. What I'm arguing is that the problem that you have when dealing with the "Norse Expansion" is that the Norse would go as far as divided politics and military prowess would allow them. As they expanded, they became thinner on the ground, and even in places where they were became the political and military leadership they were quickly assimilated. So although you may put Norse leaders in Flanders, Normandy and Brittany, so what? They will be just as French as the people they exhorted the land from within a generation or two anyway.
Now if you have a hardened Frankish Empire, then this will concentrate those Norse wanderers. The English will probably fall relatively quickly, and the cultural change probably won't be all that drastic. The Anglo-Saxons, who made up the overwhelming majority of the English population, being a Germanic people, were very cultural and linguistically close to the invading Norse, who were also a Germanic people. So England is added (or perhaps re-aquentancied) quickly to the Norse cultural and political sphere. Now England is a base, rather than a destination, for Norse vikings, merchants and explorers. With the population base the English Norse kingdom will have they will be able to launch a serious bid for leadership of the Norse world (vs. Denmark), and (more importantly) contest with them for overlordship of Iceland (and thus the Far West).
More importantly, without Britain as a disunited refuge for any blackhearted villain from Scandinavia, relocating to the Far West might not look like a bad idea.
Exactly. Except it wasn't blackhearted villians, it was losers in the endless Norse wars of succession who provided much of the Norse population willing to permanently move to new lands.
You're headed in the same direction as me, but I have a vision of two different threads of Norse settlement. One follows patterns similar to OTL's New World colonies, perhaps starting a couple hundred years earlier, with resource exploitation colonies followed by permanent settlements.
That is so old. The pagan religion was only strong where it wasn't challenged by the Roman Church. If you have the Mesoamerican civilizations discovered, that will set off a wave of Norse settlement, the news will spread far and wide, and you can bet that Roman Catholic priests will be among those who come West. Paganism is cool and all, but Christianity beat the hell out of it for a reason. It is much more politic to be a Christian (Monotheist in any case, Christian in this case).
The pagan Norse and aforementioned blackhearted villains will head up the rivers, especially the St. Lawrence, and create a creole culture that has lots of quite recognizable Viking cultural traits.
Though the Norse interbred and assimilated in various European locales, that didn't happen in Greenland, the only example that we have to work with of Norse interaction with a North American native culture (the Vinland examples was also one of a distinct lack of assimilation). While I can see cultural give and take with the quite advanced mesoamerican civilizations I don't see the Norse having the same give and take with the natives of northeastern North America circa 800 to 1200 AD. These were not technologically or culturally advanced peoples. The Norse would ride down the St. Lawrence as slave-raiders, gathering natives for European pets or Norse plantations far to the south. I don't see a creole culture arising around the Great Lakes.
For a creole culture, I would look to the Norse mercenaries that the mesoamerican polities are going to be hiring. Lots of fun.