The response from Moneris is supposed to be XML. That's configured in the hosted configuration. This is done by setting "Response Method:" to "Sent to your server as a POST containing XML". Check within CBSubs > History Log to see what the response was. There maybe a PDT logged in CBSubs > Notifications as well with the response Moneris sent.

I've to admit the guesswork of their API implementation is making me consider dropping support for Moneris. They need to give me a guaranteed outline of what will happen, because this is not maintainable. Also would help if I could even find their API documentation for CA implementation again, but they're all dead links so at this point I don't have a clue what to expect in the gateway anymore.

I haven't done any updates to PayPal Pro recently. It should still work, but if it doesn't it's significantly easier to maintain as I've a full testing environment for it and access to all their detailed documentation. PayPal Standard, Ogone, Authorize.net, and 2Checkout are probably the most used and recommended gateways we provide. Regardless if you run into PayPal Pro issues we can at least fix them. As for Moneris I still can't find the CA implementation documentation so I've no idea what to suggest at this time.