ראה, נתן ה' אלו-היך לפניך את הארץ עלה רש, "See, the Lord your God has given the land before you. Ascend and take possession!⁠" Instead of the word ראה at the beginning of this verse we would have expected the words הנה נתן ה' אלו-היך לך את הארץ, "Here the Lord your God has given you the land.⁠" Why did Moses change the usual syntax? He wanted to indicate to the people that seeing the protective angel of these people had already been dealt with by God, the people themselves should certainly not present any obstacle. All the Israelites had to do was ascend and take possession. The word עלה is to be understood as "climb on to, or over the protective angel of these people who had already been brought low.⁠" The word ראה here refers to the mental eye of the people, their ability to understand the situation of the Canaanites after the Lord your God has already given the land "before you,⁠"

This is also what prompted the sages of the Midrash (Tanchuma Massey 4) to write concerning the above words: "did then God literally place the land of Canaan at the feet of the Jewish people?⁠" They answer that the meaning is that God made their protective angel fall to earth in front of the Jewish people. This is why we find similarly worded verses in verse 8 of our chapter, and a similarly worded report in 2,33: "go and take possession of the land" had been used in verse 8; the Torah, at this point should have written only: "take possession of it,⁠" instead of repeating the words את הארץ. The apparent repetition means that an obstacle which had existed in verse 8 had meanwhile been removed; the obstacle was the protective angel of the Canaanites. Rashi makes a similar point in explaining the wording of Deut. 2,31.
As to the word החל רש used by God in 2,31 as compared to the word רש without the preamble החל in our verse here, God meant that seeing He had commenced giving possession of the lands of Sichon to the Jewish people (at the time), it was now time to complete the work of taking possession of all the lands of the Canaanites and to complete the process. This is why in our verse the word החל, "begin!⁠" would have been out of place. There was no reason to add the word גמור, "finish, complete,⁠" in our verse because as soon as the Israelites would have commenced to do their part (if the report of the spies had been uniformly favorable) the whole campaign would have ended almost as soon as it started. When God commences a war, it does not last long.
We have a Midrash Rabbah in Exodus 21,5 in which the same point is made concerning the demotion of Nevuchadnezzar of which Daniel speaks in Daniel 4,28 when a heavenly voice announced that the king had already lost his kingdom (although he still occupied the throne and bragged about his accomplishments). Rabbi Joshua ben Avin interprets the words קל מן שמיא נפל in that verse as "an angel named קל, i.e. Nevuchadnezzar's celestial counterpart, had fallen from heaven.⁠" This is why the verse in Daniel did not speak about a voice from heaven being heard, or calling, but "falling.⁠" It was not "a voice" but that angel. Immediately after that, heavenly voices saying: "your kingdom Nevuchadnezzar has departed from you, (and much worse)" were heard.