Depends how much difference there is.

My first name is abbreviated on all my Air Canada tickets but is spelled in full on all my other ID, including passport. They said they were going to crack down on this last year, but I have had no problem to date

If the difference is significant, it could pose some difficulty. Even when you do enter properly though, AC often incorrectly merges the middle and first names on the ticket anyway so I am not sure it is that big a deal.