Evolving Wurmple - Cascoon or Silcoon?

It's supposed to be completely random. Nothing can be done to influence the result.

Don't worry about it too much. There's only two outcomes, it only costs you 12 candies to try, and Wurmple is fairly common. Neither of the final forms are worth anything in the meta either.

I evolved one of each using the old Eevee trick.

Name them May and Jessie. It worked for me. Please let us know if it works for you.

https://m.bulbapedia.bulbagarden.net/wiki/Wurmple_(Pokémon)

There hasn't been any trick found, but they seem to be very common under certain weather conditions, so I'm not sure it's worth worrying about too much.

I got one of each with the only two I've evolved.

I evolved 5 x Wurmple and now I have 5 x Silcoon and 0 x Cascoon.