One of our regular commenters on our site, Britney, linked to an Italian Vanity Fair article (from Feb 8) with Owen Wilson and during the interview he mentioned that he's back to do the voice of Lightning McQueen in Cars 3. This isn't really a shocker, but it's still nice to read that it's confirmed and that it's not Keith Ferguson who voices Lightning in the Toons.
Owen Wilson's note (translated from Italian)
After Zoolander No. 2 will work on a new sequel ...
"Yes, I will return to give voice to Lightning McQueen in Cars 3. The funniest part is when I meet children and parents explain to them that it is actually my voice to Lightning. I always look warily, then burst into tears. "
What's weird is that the way Owen commented, it's almost like he hasn't recorded lines yet...but at this point, unless they're touch-up lines, the bulk of the recording would have already been done. I mean, Ellen recorded her first lines for Finding Dory in September 2013 and Tom Hanks just noted that he's already doing his first session for Toy Story 4. It could just be coming across wrong because of the translation, or Owen could just be being vague. I'm going to assume that's what it is and that he's already recorded the majority of his lines though.