One of the geological mysteries noticed is the Hudson Bay Arc. It is quite perfectly shaped, but the reason is not known. The edge of the Icelandic shelf platform is also an arc, but under the surface of the ocean, so it is less noticed on maps.
As can be seen on the maps, the arcs are identical. It does not necessarily mean that the two topographical / bathymetrical features are originally formed in the same way.
I have already examined the Icelandic Arc in detail in other posts. The Hudson Bay Arc is much more difficult to study, but this might be a clue for others to investigate further. https://magicmagma.com/2020/03/04/the-symmetry-of-iceland-around-the-reykjanes-ridge/
See also: https://www.mentalfloss.com/article/609355/geological-formations-baffle-scientists