PayPal is an e-wallet that sits between your bank account or card and the merchant, so the casino never sees your card or banking details. For gambling it is selective. Its Acceptable Use Policy lists gambling and casino games among activities that need PayPal's pre-approval, and it only covers operators and customers located in places where the activity is permitted by law (PayPal Canada).
That is why PayPal shows up at some regulated Ontario casinos and not others. If it is available, you pick PayPal in the cashier, log in to your PayPal account, and approve the payment. Withdrawals, where offered, are paid back to your PayPal balance, and from there you move the money to your bank.
Check two things before you rely on it. First, the casino's withdrawal options, because a method listed for deposits is not always available for payouts. Second, PayPal's own fee schedule for your account type and any currency conversion, since PayPal sets those charges, not the casino. Seeing PayPal at a site is not a substitute for checking the site in iGaming Ontario's directory.
Source: www.paypal.com