To confirm some of the explanations in the other thread:
Names of regions and countries as used by earlier authors, particularly Linnaeus and his contemporaries, do not necessarily apply to exactly the same regions and countries as possess them today. Sometimes they were vaguely applied; often boundaries have changed. Many have become obsolete. […] `Canada in the Linnaean sense does not correspond to the modern Dominion of Canada but to a region of north-eastern America, partly in Canada, mostly in the United States, where Kalm did much collecting’.
– From Botanical Latin, 4th Edition, by William Stearn.
Canada, Virginia, and Carolina particularly fall into the ‘vaguely applied’ category.