One of the new features I've seen listed for Windows Phone 8.1 is the ability to sync with Google Calendars with multiple calendars. I've seen this in effect on my GMail account, but it doesn't appear immediately available on my Google Apps account. I've already gone to the iPhone Sync Settings page and verified that the calendars are enabled for sync (most already were, so I just added the couple I wanted that weren't). Are there other steps I need to do - anything special for Google Apps accounts?
As I am new to Windows Phone I can only tell how I did the sync with my Nokia Lumia for the Google Calendars, but maybe it helps:
1. Add Google Account to Windows Phone Accounts
Therefore go to Settings --> E-Mail Accounts and other and add your Google Account
2. Make sure the calendar data will be synchronized
After setting up your Google Account in the phone, click on the Google Account for more detailed settings. On this page you will see a select field called something like synchronize contacts and calendars where you can change the interval of sync. Then there is also left to choose the contents to be synchronized where you have to check at least calendar.
3. Check the Google calendars you want to be synchronized
For that purpose go to the native calendar app of your Windows Phone and go into the settings. Now you should get a list of calendars of your Google and your Microsoft accounts which you can check/uncheck however you like and also set a color for every calendar.