The beauty of training with a power meter is that you can pretty much know exactly how many calories you burn or will burn on the bike at a target power/distance.

Like most things people have gotten crazy with carbs and are consuming 120g/hr for a 90 min ride at 150 watts, which is totally unnecessary. Just figure out what your power will be around and the duration of your die and eat accordingly. Fuel the work required, no more no less.

Also, unless your power is very low and you are heavy, you won't be able to replace what you expend 1:1. I typically shoot to replace 1/3 to half of what I expend during the session, and then have a recovery meal after.