Google Wallet cannot hold a balance. So you can't "transfer over".
The PayPal link allows Wallet to charge to PayPal for select transactions.
If you have a debit/credit card issued for your CashApp account, you may be able to add that card to Wallet and then pay with it. That's what I do with my Venmo account.
Unfortunately, you need the card to do that since you will need the account number and the security code.