Hard to say As I have not played this battle level
If the tanks are starting on turn one in LOS of AT gun it is a badly designed level and not worth playing IMO/
Of course knowing there is any AT gun out there is a big advantage
But still if AT guns are quite common If I was in A tank platoon
I would always assume their is AT guns out there
If you have Artillery USE IT in turn one especially for Soviet as it can be slow and especially if it large calbire, where you think enemy is and ht them Smoke or HE what ever is best
USE Cover Arcs on your Tanks , narrower the better this will help with spotting the gun
Send one infantry or one tank ahead first to draw fire and/or spot the gun or gun site
USe Area fire against suspected At gun sites ,
creep up to position within LOS of front edge of Known ATG and HIT it with Area fire i.e. Indirect area fire against the gun position You can hit area close to ATG but it cannot see you BLAST Away it will suppress and knockout gun.