You can’t get away from religion in "The Tyger." In Blake’s day, religious individuals and their institutions held great sway over people, far more than they do now in Europe. Questioning God’s absolute supremacy was pretty rare, and was all but political suicide. Blake, on the other hand, has no problem questioning God, or dabbling in religious arenas that don’t automatically assume that the Christian God is actually alpha and omega ("the beginning and the end" of the Greek alphabet). Thus, Blake questions who "could" create the Tyger, casting aside the notion that such a being is omnipotent (all-powerful). He also challenges he who "dares" forge the Tyger, and contain ("frame") its "fearful symmetry." Blake is not afraid of religious visions, since this poem is full of them, but he's not interested in simply rehashing the Christian doctrine. Rather, he interacts with Christian religion by challenging its assumptions.
God, "he," is the creator of the Tyger; thus, since Blake calls into question the creator’s authority and courage, the poem questions the basic assumption that the Christian God is all-powerful.
The Tyger isn’t a creation of God at all, but is God himself.