I have moved the topic to the Anniversary-category. @barnee is correct.
This question is part of the official FAQ:
Q. Are sea zone 1 and Western Canada adjacent?
A. No. The gold map border obscures the fact that the Hudson Bay area of sea zone 1 doesn’t quite
reach all the way to the western edge of Eastern Canada.
I agree with your rational, but I do feel that Paratroopers belong in the game. I don’t know the solution though. Perhaps they could only be used in attacks where at least 1 other unit is also attacking the same territory by land or by sea. (I would make an exception for islands and perhaps undefended territories.)