One is the Establishment choice, the status quo, ahead in all the polls and favoured by most of the media and the 'experts'.
The other has risen by tapping into nationalism, populism and a thirst for anti-Establishment rhetoric. While the rest of the world looks on, shakes its head, and tells voters that it would be a reckless move, many think it will make their country "great again".
But the similarities between Britain's referendum on EU membership and the US presidential election don't end there.
Bookmakers recently slashed odds on Donald Trump winning the election following a betting pattern that was "eerily reminiscent of those seen in the lead up to the EU referendum" - the greatest volume of money going on Hillary Clinton (just like Remain), but the greatest volume of single bets going on Trump (just like Leave).
But perhaps the clearest sign the election result could be the unexpected one was a tracking poll by the Washington Post and ABC News this week.
It showed that Clinton held a 4 point lead over her rival, a gap that had narrowed by 8 points and one that is likely to continue narrowing following more revelations about Clinton's emails.
Perhaps more significantly, and somewhat worryingly for Clinton, was the poll showing the "expected result".
While she only holds a narrow lead in the poll of likely votes (above), the majority of Americans (59 per cent) think the Democrat will win.
Like the Brexit vote, where many assumed Remain would win, those figures suggest shy Hillary supporters may not bother turning out to vote if they think it's a foregone conclusion while shy Trumpers will.
As the film director Michael Moore said:
He is saying the things to people who are hurting. It’s why every beaten down, forgotten, nameless stiff who used to be part of what was called the middle class loves Trump.
He is the human Molotov Cocktail they’ve been waiting for. The human hand grenade they can legally throw at the system which stole their lives from them. On November 8, the dispossessed will walk into the voting booth, be handed a ballot, close the curtain and take that lever and put a big fucking ‘X’ in the box by the name of the man who has threatened to up-end and overturn the very system that has ruined their lives: Donald J Trump.
Trump’s election is going to be the biggest 'fuck you' ever recorded in human history. And it will feel good.