Unfortunately, Google and Hi-Rez accounts cannot be merged. Google and Hi-Rez are two separate companies and have separate databases. All users who have accounts with either company would need to use the separate account credentials for their respective services.
However, you may link your Hi-Rez account to your Google account, which may allow for data transfer and other functions (available games depend on the titles in question). To link your Google and Hi-Rez accounts, please follow the steps outlined by Hi-Rez in this article: https://help.hirezstudios.com/hc/en-us/articles/219400887-Link-Google-Account-to-Hi-Rez-Account-
For any additional questions, you can reach out to the Hi-Rez Studios Support Team by creating a support ticket here: https://support.hirezstudios.com/