This is "like the scent of a field" (Genesis 27:27): he foresaw that he was destined to stand and build Zion and to offer sacrifices in its midst, and so he blessed him. And "a field" can mean nothing other than Zion, as it is stated, "Zion shall be plowed as a field" (Micah 3:12). "Which the LORD has blessed" (Genesis 27:27) — that is the one of which it is written, "like the dew of Hermon" and so forth (Psalms 133:3).
Isaac Smells the Field of Zion in Jacob's Blessing
Midrash Tanchuma Buber, Toldot 10:5
דא כריח שדה, צפה שהוא עומד ובונה ציון ומקריב קרבנות בתוכה וברכו, ואין שדה אלא ציון, שנאמר ציון שדה תחרש (מיכה ג יב). אשר ברכו ה', אותה שכתב בהו כטל חרמון וגו' (תהלים קלג ג).