Bettors (Punters) will give you the odds on anything and put their own money on being right. Pollsters do as well although there's less of a premium on being right the further out the outcome is. So what the heck, here is a site set up in England where this sort of thing is legal that posts the odds for all the primary candidates as well as for the general election.
A word of warning would be that the earlier in the campaign you are, the more you run the risk of a "black swan" event happening downstream that turns everything upside down. Still, they are currently giving Hillary a 56% chance of winning the general election with Rubio the most likely pick to be running against her.
Election betting odds is updated every 5 minutes for your enjoyment. Bookmark the link and check back around the first of each month.