Your Google Calendars won't sync with iCloud. The two are entirely unrelated services. However, you can do a couple of things as a pseudo work-around.
In one sense, if you have your Google Calendars on the iPad, they'll automatically sync with Google calendar and any other device that's configured to read the calendar.
Another option is to use something like BusyCal to combine the Google and iCloud calendars. I wouldn't recommend this, as it's a much better idea to keep the data from the two services seperately.
Your main decision is to which will be your main calendar. It's solely a personal preference, as both calendars will largely give you the same functionality. If you prefer editing your calendars on the web, maybe stick with Google calendar. If you want to be able to share calendars with other iCloud users, move to iCloud calendars.