Pre reboot, it's a close one. They're sparring partners for a reason, and Diana should get the benefit of the doubt because of where she grew up, in the same way Martian Manhunter could get the benefit of being a skilled telepath not only on feats, but because he comes from a culture that's refined the art of telepathy over centuries...
When they fought with staffs, and Canary won, she thought Diana let her win. So it's close, definitely an either-can-win thing, but probably small edge to Diana.
When was this? I remember both characters sparring in Birds of Prey. If my memory serves me correctly, Diana defeated Dinah. I might be wrong of course.
Overall, I give Diana the majority over Canary. Don't get me wrong, Simone gave Dinah a huge push. But, compare to Diana she's still second best. Diana was trained from birth to be a fighter. She's sparred with Donna Troy, Batman, Superman and in fact considered one of the best hand-to-hand fighters by many.