The M4 Shermans in WoT at the moment are only armed with the classic 75 mm, the fast firing 76 mm guns, and the 105 mm howitzer. In lieu of foreign weaponry such as the 17 pdr or the French 105 mm, WG has already likely modeled a 90 mm armed M4 as seen below.
This particular vehicle, called the M4 90V by WG, was built in 1944 in order to have 90 mm armed tanks in order to give American tankers a weapon that could more easily defeat German armor. I have not found an official designation of this vehicle in my resources so I can only assume that WG’s name is acceptable.



