Well, remember, AG, that what we are concerned with is specifically what Cloud's romantic intent is.
There's quite a lot of different quotes telling us he feel secretly in love with Tifa before leaving Nibleheim, that he leaves for SOLDIER to impress her, that he has his promise to her etched on his heart, that seeing her again brings him out of his coma, that 'only [her] opinion matters', that their hearts called out to each other, that they became aware of the mutual feelings they were holding, that 'words aren't the only way' is risque dialogue, and that Cloud thinks he can succeed in life where once he had failed because Tifa is with him. We know Tifa is someone's lover/ sweetheart, that Cloud is her love interest.
We know that Cloud has opened his heart only to Tifa. And that is simply off the top of my head.
The evidence for C/A is not so concrete.