The example shot looks like it's suffering from two main issues.

1. White balance is coming out very much on the blue side. When we think of 'sunny' we think of 'warm'. Humans equate orange with warm & blue with cold.

2. It's over-exposed. The camera was presumably thinking the tree was the main subject & tried to deal with that. Unfortunately, cameras don't actually 'think' so you have to do some thinking for them & compensate in such conditions where there is a high contrast between shaded & sunny areas.

If you look at the original histogram, you'll see there's a lot hard to the right - the sky is completely blown-out, no way to recover that.

I ran the pic through Photoshop, & simply hit 'Auto' to see what it could do. I also changed the white balance using the bit of the dress visible between the chap's legs.

These are the changes it made -

& this was the result -

This was literally one minute's work. You could do better from the original image & a bit more care & attention to detail.

It looks 'warmer' therefore you interpret that as 'sunnier' & we've gained a little definition in the foreground.
The background is less successful. The sky is gone forever, there's no detail there to recover. The water, similarly, is so near to blown that there's not a great deal can be done for it.
The trees in the distance I think are acceptable like this. They're not sharp because of depth of field - it would look odd if they were sharp at that distance [mobile phones do things like that which makes things look very awkward] & they're no longer buried in blue haze. They're a bit under-contrast. If you were convinced they needed more you could mask it in, but as they're not the subject of the photo, I'd leave it.

You could go for a bit more punchy - those three 'magic' sliders at the bottom, Texture, Clarity & Dehaze can punch images up so far they hurt.

This is everything set to +20 …already too much, but just as an example -

One other thing you could possibly have done would have been to use a polarising filter. That could have cleaned up the water & added definition to the sky.