How can I remove the sun glare from this photo? Is it possible?

It's probably easier to do now than in was in 2012. I just ran across this post and had to give your image a try.

Steps taken:

1. First, I used the ruler tool to level the photo - using the horizon line (where the sky and water meet) as a level. Then, I cropped it so that the horizon line meets the vertically "one-third" from the top and the couple is centered horizontally.
2. Next, I created a new layer and hand-painted the brown shirt over the "faded" section due to the lens flare. I selected a brown color from the bottom section of the shirt. (This can be done with an even cleaner transition, I was trying to do this quickly.) I set this layer to "overlay".  Use a layer mask to keep this effect where you want it.
3. I added an adjustment layer and played with the levels until I was happy with the results. (Layer > New Adjustment Layer > Levels...) My result looks a bit posterized, so you'd have to play with it some more if you don't like that effect.
4. Finally, I used the clone stamp tool to paint the "faded" water, using [Alt] and clicking where I wanted to paint from (the darker blue water.)

There are a large variety of ways to make corrections such as these, but here's my stab at it:

Was a fun picture to tackle! I'm surprised you didn't get more interested in trying to manipulate it.

Here's my try. The glare spot in the sky is burnt with 0 color values, I guess due to the 8bit compression and can't be pulled out without creating new values. I tried Content Aware fill and it worked well on a rough selection of  the spot. I only had to paint touch the wall at the left.

The shirt, I painted over. Depending on the image and detail, I often spend less by painting over than using global adjustments. I just selected the shadowed (front) part of the tshirt use levels to darken a bit on a new layer and smoothed the transition with a soft brush, Then I painted some wrinkles with the brush referring to the original in a window beside. Then I added some sharpness and lighting on additional layers masked them out then reveal partially the mask by painting with the soft brash to lighten and sharpen some areas like the faces. I also pulled some details from the sky by using the shadows/highlights. Played about 15 min with this.

       Click on this thumbnail for larger (50%) image.

100% MAX Quality 5.9 MB JPEG at:  http://dl.dropbox.com/u/57727070/DSC04203_optmzd_MAX.jpg

As Lundberg02 says, you need to learn Photoshop.

Not exactly a 'fully sunglare removal' but hope this helps.

Clone Stamp tool, Color burn and Curve Adjustment with Tone, Color & Contrast adjustments in under 5 minutes.

This is what I came up with:

Of course it's possible.  The problem is mostly white balance and gamma adjustment. Read up on using Photoshop.