You can synchronize Google Calendar and Google Tasks to any On My Mac account in the Calendar app and Reminders app on Mac OS X.  The Mac has the ability to set up Google Calendar, but only as a separate account from the On My Mac account. With CompanionLink, you can fix this.

1. Download CompanionLink for Mac. It’s available here.
2. Configure it to sync with a free DejaCloud account.
   1. Tip: you can set up Auto Synchronization to make it automatic.
3. From Advanced Settings, choose the Mac Calendar account and categories to sync.
4. Log into the DejaCloud web portal and enable the Google Connector.
   1. Click Account Status.
   2. Click Connectors.
   3. Click Add Google Account. Enter your Google login information.

Here is a full setup guide for further details.

Your Google Calendar and Tasks data will now synchronize to the Mac Calendar account you specified in Step 3.

CompanionLink for Mac is free to use for 14 days. If you need uninterrupted synchronization, a one-time license costs just $49.95.