Gibb, I don't think anybody would call you naive about any of this :). Perhaps I am reading back into history something that was not there at the time, but it makes sense to me that "land of Canaan" stands for something like "God's gift", "the promised land", "the place of abundance", "flowing with milk and honey", etc. All of which might "soon be a-showin" if Sally doesn't "keep her legs togedder"...   "Hi-lo, John Brown, stan' to yo' ground!"   I suspect that the "sacred and profane" were not so very far separated if we look at this from either a religious perspective and/or an "African-American" perspective. I don't find it unusual or out of place for a so-called religious/theological concept to show up in a bawdy song as a potent metaphor.

For an interesting update on this check out the Indigo Girls (their use of the metaphor is a bit different but perhaps related):

http://www.metacafe.com/watch/sy-14210989/indigo_girls_land_of_canaan_official_music_video/