Do not dilute with water, peach wine is light enough as it is. You could use the juice from the canned peaches, but be prepared for the S.G. to bump up since you will be adding more fermentable sugar---are you adding natural, light, heavy syrup from the canned peaches? Another option is to top up with shelf stable Welch's White Grape Peach juice (typically comes in 64 oz container).
In the future, try to get in the habit of making a "topping up excess" amount--just takes a little extra adjustment on your recipe.
Motto: quel che sara sara