Firstly, this is really, really excellent stuff. I've never seen a Pre-Columbian contact TL handled so artfully. Really well done, it simultaneously retains elements of the fantastic that so often dominate such timelines with a sense of realism that keeps the whole thing from staving into ASB. Fantastic.
Now that that's out of the way, I'm rather surprised that other Monastic orders didn't get in on St. Brendant (what I refer to Insulam Benedictus as in my head, as that's always how I've referred to the illusory Isle of St. Brendan). Their were plenty of Pappar who were pretty psyched to go to empty desolate rocks in the North Atlantic just for the opportunity to get some peace and quiet IOTL: St. Brendant provides that in spades, along with some really quite stunning natural scenery to aid in contemplation. Not only that, it would be contemplation in a place that is literally regarded by Christendom to be in some measure holy, being the isle of the Saints. Not only that, it provides an opportunity to save souls in spades, at least in theory. Not only that, it provides (most importantly) a great source of the almighty ducat. Add to all of this that the Pappar are probably better set up then anyone to sail the North Atlantic. I really don't see why there wouldn't have been a monastic bonanza prior to the private fur-trapping bonanza.
Thirdly, and off the criticism, the Viking expansions will truly prove interesting times. With the North Atlantic already mapped and sailing it already thoroughly understood, the Vikings are going to get their quick, and superior ship building is going to give them a massive advantage. The Insulam provides far greater economic opportunity then Iceland or Greenland, and even ignoring the fur trade, far more fertile fields. Ironically considering the exploration's Christian origins, this provides a much better opportunity for the survival of Viking paganism then the Vinlandic TLs which attempt to do the same, as by the time the Norse are arriving they won't have been fully Christianized.
Finally, and perhaps making for the most fun (or stretching of credulity, for more cynical readers), since the Maritimes are already fully discovered and charted, the Vikings are going to be doing exploration much further afield then OTL. The Kensington Runestone is no fake ITTL (and Runes may well be the predominant script of NA, since I don't see Ogham catching on), and Longships are going to be coming into conflict with proto-Powhatan. Berserkers chewing on fat cigars? Maybe the *Knights Templar gets redirected from the Holy Land to fight this marauding menace and sets up shop in Newport.
It would be cool to see a major port arise at the mouth of the Penobscott, considering the excellent access it provides to the interior, its excellent timber and harbors, and as a nod to
this