I would think the bracha on Maple syrup would be ha’etz. They are often planted specifically to harvest the syrup; this, then, is their fruit. The liquid state is, of course, irrelevant.
It seems to me that maple syrup would not be much different than sugar extracted from sugar cane or molasses extracted from dates, which in both cases the Shulchan Aruch and its commentaries say that the Bracha is "shehakol" since it is not considered the fruit itself. ( שולחן ערוך או"ח סי' רב סע' ט"ו)) However, the Taz (based upon the Tur contrary to the Rambam) in his commentary there ( סי' רב) seems to allude to what your'e saying. However he himself does not say to make "borei pri Ha'etz" on sugar, but if one were to make the Bracha on fruit he would be "yotze" for the sugar which is the "fruit" of the sugar cane. However, great poskim have decided that in regard to sugar which is extracted from sugar cane, the prevalent custom is to make a "Shehacol" as the Rambam decided contary to the Tur. (שו"ת משנה הלכות חלק ו סימן לח) I therefore uphold what Rabbi Lewis wrote that the "bracha" for maple syrup is "Shehacol."