Parashas Masei · Passuk 34:15 · TT note 1
Chabad.org — English translation + Rashi
Torah Temimah points to Bechoros 55a (TT note on “מֵעֵבֶר לְיַרְדֵּן יְרֵחוֹ”).
E-Daf — Bechoros 55a · Sefaria
English: “Across the Jordan of Jericho” — he equated the Jordan with Jericho: just as Jericho is the Land of Canaan, so the Jordan is the Land of Canaan.
Gezeirah shavah / hekesh — Jordan equated with Jericho for the status of the land.
The eastern bank of the Jordan that was settled by Reuven, Gad and half-Menashe is treated as part of the Land of Canaan for the relevant halakhic purposes of the border description.