So...Saitama vs Sho Fukamachi as the gigantic. 

 

Could the gigantic stand up to the man who can destroy things in one punch?

 

Considering that Saitama's Serous Punch totally overpowered Boros's Collapsing Star Roaring Cannon, an attack that can destroy the surface of the earth (or blow up a planet in the anime), Gigantic's weapons are no threat to the Caped Baldly.

That said Gigantic Exceed's  Gravity Implosion should work... if it was given time to fire it. The problem is the attack takes time to charge and Saitama generally has little patience.

Depends on the venue, like with Goku. In his own universe, Saitama is invincible except against King, but in the Guyver universe he might be just another drop-out sarariman.