The only possibility is the BL Ordnance 6-in gun (not howitzer) Mark VII- not sure of the carriage (four types which one this is hard to tell -MkII?). It was originally a naval gun.
Some plans on the Landships Forum ( by Ken Musgrave). This was a very big gun eg the wheels are about 5-6 feet high and the weight in real life was over 25 tons. When fired the wheels rolled on to "scotches" which were large wedge shaped pieces with a slight curvature to take the recoil these should really be included in the set as firing without them would be fun (on the plan referred to above).
The wheels and some details could be rethought after looking at the plans referred to above and it should be made in polystyrene (hard plastic) for super detailing and sturdiness.
BTW getting the name right is important as internet searches will prove fruitless otherwise. I would guess it should be item A003( the real one as there are 2 A003s at the moment) and it should be gun not cannon.
Well done Strelets a nice development. The Mark XIX gun (A004) was also a 6 inch gun but on a similar carriage to the Mk VII Howitzer .
These really do look the part. It's great to see someone finally making artillery men who actually look as if they are doing their job rather than looking like they are straight of the Parade ground.
Best of Luck with this new venture Strelets, I'll be buying.