It is not an either–or. You may have certain rights under both CCPA and GDPR, but they have rather different mechanisms for determining their scope.
When does the CCPA apply?
CCPA applies to certain businesses and consumers. It covers any business (regardless of legal structure) that that does business in the State of California and has a certain scale. A consumer means a natural person who is a California resident.
These aspects are not influenced by your current location. When you as a California resident travel to the EU, you still have all your CCPA rights against businesses that do business in California. You do not have any CCPA rights against businesses that don't do business in California, for example a national rail company in the EU you've bought a train ticket for.
When does the GDPR apply?
Whereas the location of the user/data subject can be a factor in the GDPR context, their residency or nationality does not.
The GDPR applies to all processing activities by data controllers who are established in the EU, including any businesses, non-profits, and individuals. This includes processing activities in the context of an EU establishment of a non-EU company. For example, GDPR would apply with respect to processing of personal data by a hotel you're staying at in the EU.
The GDPR also applies to non-EU data controllers in the context of (a) offering goods or services to people who are in the EU, or (b) monitoring behaviour of people who are in the EU. Here, “offering” does not mean “doing business”, but “targeting or marketing”. For example, you might have installed a smartphone app that assists with sightseeing while in Paris. If this app monitors your behaviour while you are in the EU (such as by tracking your GPS position to alert you to nearby points of interest), that would fall under the GDPR while you are in the EU. The app may also fall under the GDPR per case (a) if it is marketed to / targeted at people who are currently in Paris.
That the GDPR applies in such cases comes from the offering/monitoring while you are in the EU, not from your continued presence in the EU. You would be able to exercise your GDPR rights relating to this processing even after leaving the EU.
Note that some service or processing activity can fall under CCPA and GDPR simultaneously.
For example, this app would also fall under CCPA if the company also does business in California, e.g. if it also provides sightseeing information for Los Angeles or San Francisco.
And both CCPA and GDPR could apply when an EU company does business in California.
Under which privacy law would a deletion request be dealt with?
In practice, most companies don't have this sorted out properly and results are unpredictable. Ideally, a company would just comply with both laws simultaneously, thus making it unnecessary to determine which law applies. Information that is only required under on law can be provided with conditional statements, e.g. “If this processing activity is covered by GDPR, you have the right to lodge a complaint with the supervisory authority in your country”.
As mentioned above, both laws can apply simultaneously. Whether GDPR applies and whether CCPA applies are independent questions. However, the answer to neither of these depends on your current location at the time of making the request.
In this answer, any statement about the EU applies equivalently to the UK.
