Update US/Canada border to use higher resolution

[camdecoster]

Description

The US/Canada border (soon to be) added in #7393 is too simplified and should be updated to show the border at a higher resolution.

NE Data	UN Data

Acceptance criteria

• The border is updated to more closely resemble the previous border shown in the maps based on Natural Earth Data
• The related baseline images are updated to reflect the change

Notes

• The source data from the UN is too simple to begin with at this border
• It will likely require manually updating the polygon borders