“beyond the Jordan.” The phrase “beyond the Jordan” can refer to either east (Deut. 3:8) or west (Deut. 3:20; 11:30) of the Jordan River depending on the context or the location of the speaker. Here in Deuteronomy 11:30, the Israelites were east of the Jordan River, so “beyond the Jordan” in this context meant west of the Jordan River.
“the Canaanites who live in the Arabah opposite Gilgal.” The Arabah is the part of the Great Rift Valley that is around the Dead Sea and north of it for 15 miles or so. It is mostly desert and scrub wilderness. The Canaanites lived “opposite Gilgal,” that is, west of Gilgal and up into the mountainous area in central Israel, and that is where Mount Ebal and Mount Gerizim are. The name “Gilgal” was added by a later editor, because the site was not called “Gilgal” until the time of Joshua (cp. Josh. 5:9).
“the road of the going down of the sun.” We would more normally say, “beyond the western road,” but exactly which road Moses had in mind is not stated and is debated. Some say it is the road just west of the Jordan that ran north-south through the Jordan Valley, while others suggest that it was the well-known road that ran north and south from Syria to Egypt.