I think with Harry anything is possible. I really do think that whoever he does marry, it won't be for the connections, the bloodline, the "suitablitiy" nor any reason other than its someone he is in love with and genuinely loves him in return and they want to spend the rest of their lives together.
Both William and Harry do not take take relationships lightly IMO. As we've see with William taking time and being sure when he does make a commitment its for all the right reasons, I think we will see the same with Harry. It may very well be Chelsy and then again over the next 10 years or so, it may be someone he's not even met yet. It will make interesting watching though.