If you like the flavor of maraschino cherries, they are pretty easy to integrate and give a great flavor and a boost in sweetness.
If you're going to pull out a gallon and flavor it, take one 12 oz jar of cherries (including the very sugary juice they're packed in) and muddle the whole jar and add it to your gallon in increments to your taste. Make sure your tools are sanitized and as mentioned earlier, sorbate and KMS up to snuff.
I added this to a Zin Blush, gave it a nice color and taste. Assuming you're starting with a clear wine, give it a couple of weeks to settle and clear, and you're good to go.
As an aside, as I was muddling the cherries, I started thinking about muddling fruit (cherries, orange, bitters, etc.) for a bourbon old fashioned and was struck with the idea of making a "Zin Blush Old Fashioned" wine, but haven't attacked that yet.
I bet joeswine has some thoughts on that!!!!!!!!