Slot in plywood
I did exactly this recently with 1/2" MDF. I used a 1/2" straight bit, clamped the two pieces together, and ran along a straight edge to the halfway point plus a sixteenth or two to account for the rounded edges. I ran it in 3 or 4 passes and it came out perfectly. If your bit width matches the thickness of your plywood (3/4"), this should work for you too. If you are using a smaller diameter, you would be better off using a template and edge bushings. Whichever way you need to go, make multiple passes, especially if you clamp the two pieces together.
Good luck with it.