This choice seer is obviously Joseph Smith. The fact that he was raised up as a prophet for "the fruit of my loins" means that through his work the gospel would be preached to the Lamanites and that many of the early members of the church were actually part of scattered Israel, particularly of the tribe of Joseph.
That Joseph Smith was a descendant of Joseph of Egypt is clear from verse 7 as well as the teachings of the prophet himself. Joseph Smith taught that the patriarchal authority belonged to the blood of Joseph and he established his father, Joseph Smith, Sr. as the patriarch of the church. In a prophecy about his father, Joseph pronounced the same blessings on his father that Jacob had on Joseph, "he shall be as a fruitful bough, even a fruitful bought by a well whose branches run over the wall, and his seed shall abide in strength" (Teachings of the Prophet Joseph Smith, p. 39, 151).
Brigham Young
"It was decreed in the counsels of eternity, long before the foundations of the earth were laid, that he, Joseph Smith, should be the man, in the last dispensation of this world, to bring forth the word of God to the people, and receive the fullness of the keys and power of the Priesthood of the Son of God. The Lord had his eyes upon him, and upon his father, and upon his father's father, and upon their progenitors clear back to Abraham, and from Abraham to the flood, from the flood to Enoch, and from Enoch to Adam. He has watched that family and that blood as it has circulated from its fountain to the birth of that man. He was fore-ordained in eternity to preside over this last dispensation." (Discourses of Brigham Young, p. 108 as taken from Latter-day Commentary on the Book of Mormon compiled by K. Douglas Bassett, p.94)