[robterrell]

I wonder if GDPR could be applied to companies I don't have a relationship with but have my data (i.e. CA-type data collection companies)?

[e12e]

The GDPR basically states that a company have a relashionship with you if they have data about you.

[sveme]

Sure. That's already possible in Germany, where any company has to provide you with the details of their knowledge about you once a year for free: https://selbstauskunft.net/