When Cana is comparing Lucy to Lisanna, she gets a sort of dreaming, endearing look on her face and stares at Natsu, thinking of him having a girlfriend. Also, the E-versions of the other
romantically involved (canon) pairings we've seen seem to be more open about their feelings - eg. Bisca and Alzak. Then we see Lucy hugging Natsu tightly, saying she missed him and was worried
about him (when this version of Lucy is tougher and meaner to everyone else), and then she practically clutches onto him in some way or form for the rest of the chapter.
While yes, LisannaxNatsu is probably canon moreso (at the moment anyway), Lisanna's dead, and I don't know if this Edoras version of her would be a replacement in any way. For the record, I prefer this ship anyway. The only other arguably canon ship (out of the major ones, anyway) is ErzaxGerard. However, GrayxJuvia seems to be proceeding nicely.
Actually, we don't even know that. It's only been implied - as far as we know, it was onesided, and Natsu was extremely oblivious, or did things to imply a relationship without realizing it (like holding her hand or something). It's definitely something he'd do.