How do I get 3/8" deep and 2" wide rabbet into 3/4" plywood with a handheld router
Consider getting dado blades for your table saw.  You can stack the blades, usually up to 1 1/4 inches, and do it in two passes.   The trick is to guard your fence with 1/2 scrap, and slightly undercut it with the dado before you start. 

You'll need featherboards for lateral positioning, and really good down force to keep the stock from bouncing up.  

If you're really concerned with the squareness of the edge, cut it a bit narrow with the dados, and finish up the final edge with the router.