As far as I can tell, all Regionals will be broadcast on an ESPN+ stream on the ESPN app (mobile device, smart TV, or other streaming device) or online (computer browser) ... and NOT on ESPN3, as ESPN announced in November (“ESPN3/ESPN+” I guess they meant “or”).
ESPN+ is a subscription platform that costs $6.99/month ($69.99/yr) for ESPN+ only; you can cancel it before the month is over (& continue watching for the remainder of the month), costing only the $6.99 to watch these Regionals.
According to the NCAA “Broadcast Information” Schedule, Nationals is also on ESPN+ … not ESPNU & ABC as previously announced!? (maybe this is incomplete information?)