Jamieson-Fausset-Brown on Numbers 34:6
the western border--There is no uncertainty about this boundary, as it is universally allowed to be the Mediterranean, which is called "the great sea" in comparison with the small inland seas or lakes known to the Hebrews.
John Gill on Numbers 34:6
And as for the western border,.... Of the land of Canaan:
you shall even have the great sea for a border; and no other, meaning the Mediterranean sea, which lies west of the land of Judea; Aben Ezra calls it the Spanish sea: it has the name of "great", in comparison of some in the land of Canaan, as the salt sea, and the sea of Tiberias:
this shall be your west border; namely, the Mediterranean sea.
John Calvin on Numbers 34:1-12
And the Lord spake unto Moses. God here undertakes the office of a prudent and careful father of a family, in fixing the boundaries of the land on every side, lest their right to posses it should ever be called in question. He begins on the southern side, where it must be observed that the district of Bashan is included in it, and all that the Israelites had acquired before their passage of the Jordan, so that this addition was approved of by God. He extends this part as far as the wilderness of Sin, and the borders of Edom, and brings it round from Kadesh-barnea to Addar, and the passage of Azmon, and, finally, to the stream which washes [228] the city of Rhinocorura, in the immediate vicin…
Read the whole note in the consoleKeil & Delitzsch on Numbers 34:6
The western boundary was to be "the great sea and its territory," i.e., the Mediterranean Sea with its territory or coast (cf. Deu 3:16-17; Jos 13:23, Jos 13:27; Jos 15:47).
Tyndale Open Study Notes on Numbers 34:6-9
The natural western boundary of Canaan was the Mediterranean coast (34:6). The northern boundary began at the Mediterranean and ran eastward to Mount Hor somewhere in the Lebanon range (not the place of Aaron’s death, 20:22-29). • Lebo-hamath: Cp. 13:21; 1 Kgs 8:65; Amos 6:14.