In order to see your Trello boards in Placker, you need to authorize your account to be linked to Placker. When you use Google in Trello, logging in with google alone is not enough.
How do I know Trello is successfully connected?
You can check your connection status in your user profile, click on 'more' in the top right corner to access your profile. The connection status for Trello should be set to 'connected'.
How can I connect Trello to my account?
Go to your profile, click on connect and authorize Placker to access your Trello data, this will automatically show the boards that are already imported in Placker.