In mage terms, the three main crossings of people to the Americas were -

1) Long before the Sundering, as humans crossed into Alaska and migrated south.

2) During the period the Tremere were a Diamond Order and pushing the Diamond into attacking Nameless Orders they wanted to eat, the largest of which was the Norse one. While the Norse were colonising what's now British Columbia. So Vinland would have been Enemy Territory at worst, and Just More Non-Diamond mages at best.

3) About 80 years of exploring America and trying to meet local mages peacefully despite...