It 'may' be easier to login to your gmail account via a computer, export your calendar, and then login to your iCloud account via the same computer to import your Google calendar. Afterwards, the results will sync to your iPhone.
If you mean sync with each other (iCloud to Google and vice-versa) then no. They will sync to their respective servers and configured devices. Besides, if you look in the Mail, Contacts, calendars setting, you can only select one calendar as the default. Therefore, if you choose to add an event to your Google calendar, you have to be sure to select the Google Calendar unless it's set as the default. It will be synced to any of your other devices that configured accordingly. The same goes for iCloud.