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Ramayana was composed in the post-Vedic period, which predates Puranic period. 

इयं सीता मम सुता सहधर्मचरी तव || १-७३-२६ प्रतीच्छ चैनां भद्रं ते पाणिं गृह्णीष्व पाणिना |

"This is Seetha, my daughter, she acquits herself in whatever duty you undertake. Take her wishfully, let safeness betide you, take her palm into your palm..."

पतिव्रता महभागा छायेवानुगता सदा || १-७३-२७ इत्युक्त्वा प्राक्षिपद्राजा मंत्रपूतं जलं तदा |

"She who is prosperous and husband-devout, will always be abiding you like your own shadow..." So saying that king Janaka then poured forth water into the palms of Rama, which is sanctified with hymns." 

We can observe from the above slokas that it was no where mentioned about kanyAdAn. King Janaka said that Sita will follow Sri Rama in all aspects - सहधर्मचरी(sahadhaRmacharI).