I've seen plenty that cut the pieces at a 45 degree angle in the corners (so you would have 3 pieces) and they look good to me. Here's an example of a wood version of formica:

It’s tricky because you have three sides to deal with. Can you go to a showroom and get suggestions?

I wish I could but I live far away from a showroom of any kind unfortunately :(

I think you have to choose which way you want the striations to go, and then you make the whole thing run the same way. I searched for photos online, and found examples of the diagonal seam method as well as the hidden, integrated seaming methods.

Examples of various seams

Hi @Neeky Bog -

I would run the pattern “stripe” horizontally along the longest wall...then I would have them continue that direction of pattern for the two “arms” of the U. I’m not sure how Formica is produced...on a roll, hard sheet, etc.,..but I’ve attached a pic illustrating what I mean, and how I would seam it in 3 pieces if it would work. With my patterning suggestion, the seams would be inconsequential.