What does "Gefen mi'Egypt Tasi'a" refer to?
Rashi: It returns and hints to Aram exiling Gefen Yisrael, that You uprooted and transported them from Egypt. This is like "va'Yasa ka'Etz Tikvasi" (Iyov 19:10) [Radak - because the expression 'Nesi'ah' is used for vines. Keneses Yisrael is compared to a vine - "Ki Cherem Hashem Tzevakos Beis Yisrael v'Ish Yehudah Neta Sha'ashu'av" (Yeshayah 5:7). "Tasi'a" is future tense used in place of past.]
Malbim: The author requests help to build the Mikdash and remove Yisrael from the yoke of Pras and Madai. He mentions Yetzi'as Egypt, for then You took a vine from Egypt and expelled seven nations, and planted them in their places.
Why does it say "Tegaresh Goyim va'Tita'eha"?
Rashi: Afterwards, You expelled the seven [Kena'ani] nations, and planted [Yisrael] in their land. Radak - future tense is used in place of past.