When I use the tax application to log into CRA website and download all the information I need, it displays that I have a certain amount of unused RRSP and when downloaded with the t4s it dramatically increases my return. Can I trust this information that is downloaded from the CRA website that is displayed in the tax application?
Yes, if CRA has that information in their files as "unused contributions" you can trust it and claim the deduction on your return.
This happens quite often if you missed claiming a deduction years ago. Because CRA gets a copy of the RRSP Contributions slips as well, they will often add the slip when you use the AutoFill service. You can always go look at your RRSP Contibutions made and pinpoint where this one(or more) is coming from. Do so using your CRA My Account.