Can't say I'm familiar with this particular dessert. Can anyone suggest a pairing with a traditional Tres Leches cake or is it better to not pair wine with this at all?

I'd go with a nice double espresso myself.

Mmmmmm, tres leches. Great stuff. I agree with wiml. Or, go with a hot chocolate made with Ibarra chocolate, perhaps spiked with a bit of Kahlua.

Mexican flan on the other hand? A sauternes might be just perfect.

OMG, I love this stuff!
There's a Mexican-oriented grocery store near me that makes several varieties of this. It's almost impossible not to take some home.
I'd pair it with a Baileys on the rocks. And then I'd explode.

Tres leches is very sweet and will overpower most late harvest wines. If you are going to go with a dessert wine, icewine might be sweet enough, but I might be tempted to try a port as it might stand up better. A nice cognac might work nicely as well. Forget serving anything dry with tres leches, it would be horrible.

Our Tres Leches is three milks with rum and vanilla. I would think an amaretto on the rocks would be good.

Almost any full-bodied white dessert wine, or medium-full amber dessert wine, such as most Aussie stickies or tawny port, should work.

This cake is big down here 60 miles from Mexico. My wife is a huge fan of it. The answer is a margarita on the rocks, real lime juice with a good tequila, rimmed in sugar. Either that or an espresso with a shot of aquavero (a smoky tequila liquor).