Anyone know where I can obtain a gpx file for Chicago marathon route this year to facilitate a pace pro plan

If you search the web you can find a map on the Chicago Marathon site. A gpx file is available from strava, so you can either draw it yourself from the map or use the map to check if the gpx file is correct. As the course is obviously quite flat, you can just try to constantly run your target pace.

Strava is your best bet.

As @RunR mentioned, the course is pancake flat, so Race Pro isn't gonna be much help. Also a good chunk of the race happens in the areas with very poor GPS reception, due to overpasses and tall buildings.

So, constant pace/effort and maybe a footpod can be a better pacing strategy. 

I tried to map the route from marathon site into Garmin explorer, but some streets send not to line up, hence the request. I'll perhaps try the strava option

Thanks for that advice. I noticed in New York marathon pace was unreliable

Almost all route planners offer the option to draw (parts of the course) manually, if it does not want to "snap" to the road/track or when there are wrong data in the map. In Garmin Explore you can click on the magnet sign on the bottom to toggle between manual drawing and snapping to tracks.

For running at constant pace on a flat course, I can also recommend a footpod. I have the normal Garmin one which works fine for that. For activities with changing stride length and frequency it is not very useful (hilly courses, interval training...).

For competitions I personally rely on the km splits (yes that's old school) and the average pace of the whole run. I never look at the current pace.

Have you looked in Garmin Connect web? There's Courses under Training, and some people might have made their Chicago marathon runs public. I can share mine from 2019, but I'm not sure it hasn't changed since then. And it's not gonna be 100% accurate because... buildings. 

There are a lot courses (>20) of the chicago marathon that you may downlod from Garmin Connect directly to your device. E.g.

connect.garmin.com/.../2243122

Try
Garmin Connect Web > Trainig > Courses
enter
Location: Chicago and click on the magnification symbol in the field
Course Type: Running
and scroll to the courses with marathon distance.

Good luck!