Use decoys and medic cards to use his spies against him.
https://gwentcards.com/
Go to the top left and pick Northern Realms. Get these cards as soon as you can.
Blue Stripes Commando.
Both Catapults.
All Three Crimson Reavers.
Also get all the decoys you can find.
That'll make you pretty damn strong regardless of who you're playing against.
Let that ass **** use his spies early and either decoy them or medic them from your discard pile to make sure he never gets that large of an advantage and try to break up your heaviest hitting stuff between rounds so it doesn't all get scorched at once.