Donnacona and the other Stadaconans that Cartier abducted lived with Cartier at his estate in Saint-Malo. The Stadaconans were essential political prisoners, allowed a modicum of freedom around Cartier's estate but kept under watch due to their value as interpreters for any future expedition to Canada. Donnacona learned to speak French quickly--certainly having two sons who already spoke the language helped him on that front. Using his skills as storyteller, he won the trust of Francis I over the course of several audiences, regaling the king with carefully tailored fictions regarding the nature of Canada in order to expedite his voyage home. Francis I was so taken by Donnacona's tales that he defended their veracity against the skepticism of the Portuguese ambassador (of course, whether Donnacona had successfully swindled the king, or whether Francis was trying to make is own colonial claims sound as impressive as those already made by Portugal is debatable). Attracting the attention of the French historian Andre Thevet, Donnacona may have inspired some of the more dubious elements in Thevet's description of the Americas, or Thevet merely used his alleged interview with Donnacona to lend credibility to his own fictions.

That's about all we know about the four years Donnacona spent in France before his death. Perhaps someone who knows more about French life in the 16th Century can use that to explain what life for a relatively well-off Frenchman living in Saint-Malo so you might get an idea about life on Cartier's estate in general terms.