Rashi on Genesis 10:19/רש"י על בראשית י׳:י״ט

1גבול הכנעני THE BOUNDARY OF THE CANAANITE means the end of his land: wherever גבול occurs it signifies end and extremity.

2באכה AS THOU COMEST - This word is a noun. I think it is a colloquial expression like that used by a person who says to another: This boundary stretches until you come to such and such a boundary.