It's hard to know exactly where these areas are today, but a lot of it is certainly known.
Also, we have differing interpretations of these borders from Kaftor V'Ferach & Tevuot Ha'Aretz.
Not very different interpretations, however. They're basically the same.
Perhaps it's helpful to view photos of these borders to help us get a better picture in our minds.
However, for those who go by the Rambam, Nachal Mitzrayim (and therefore, the southernmost border of Eretz Yisrael) is the Nile:
The Northern Border of Eretz Yisrael
Tevuot Ha'Aretz pinpoints Eretz Yisrael's north-westernmost border of Mount Hor as just north of the Lebanon Mountain Range, around modern-day Tripoli, Lebanon.
This is the Lebanon Mountain Range, the northernmost part would be that border and included within the territory of Asher (and also possibly Naphtali to its eastern side):
The Western Border of Eretz Yisrael
HaYam HaGadol (the Great Sea—the Mediterranean Sea)
The Eastern Border of Eretz Yisrael
The Southern Border of Eretz Yisrael
Well, there's a settlement in the Negev called both Kadesh-Barnea & Nitzanei Sinai:
(To my great frustration, I could not find even one free photo of anywhere in Northern Sinai, let alone that specific location.)
The closest thing I found was one of Israel's most southern towns, Nitzana, which lies not far from today's Sinai-Israeli border:
(If so, that would explain the incredible sense of tranquility found there—never experienced such a thing anywhere else. Just the entire place is permeated with that feeling. I'm not the only one to feel this either.)
Hope you enjoyed this photo-documentary of the God-given Biblical borders of Eretz Yisrael as defined by the Torah.