Rob Ford's Mayoral Opponent Vows ... I'll Show You Crack!

Mayor Rob Ford has some stiff competition in his re-election bid ... in the form of porn star Nikki Benz

The XXX Toronto native tells us she's serious about her run -- and she's about to turn in the necessary paperwork.

Ford's team is urging him to run for re-election, which is problematic because he just entered rehab Wednesday for drug and alcohol abuse.

As for her position -- she's a true missionary ... promoting equality year round. Check out her campaign video.