Rough ideas on what cx type tyres will fit my 2014 giant defy 5?

Narrowest CX tyres these days are 30mm and you’ll likely have mud build-up under the brake calipers on anything mildly moist. You might get away with a semi-slick like a Michelin Jet but CX bikes have much bigger clearances

None-there isn’t really enough clearance & if you can squeeze them in, you run the risk of jamming little pebble’s up in the brake callipers.

I’ve been investigating the same. In 25/26 which will fit, you can get Vittoria open Pave, or Panaracer gravel King. The latter according to reviews is by far the best off road.