Need Really Good iPad GPS

OK, I need advice. I have just returned from a trip to Canada and am really disappointed with my GPS software...I am looking for a GPS program for the iPad that is professional in nature...I need good detailed maps. marine charts, the ability to measure distance, and any additional features available...I am willing to pay a reasonable price for such a program...Can someone recommend such an app/program? I have tried every app in the App Store and have not found what I need. Thanks a lot!