It will fit, if there is space. Overhead space for roll-ons goes quickly, especially on commuter flights. You don't mention the route - on transborder flights at least I don't believe gate check is an option
I will be on a weekend early morning flight LAX-YVR. And I am Continental Gold Elite. Do I board in the first or second group? Hopefully the space will not run out by the time I board. What is that chance?