Sorry, If I'm late to this conversation, but...
No, I'm afraid you can't use the old Italeri M4A1 for any Canadian vehicle. It represents the late hull M4A1 with the large hatches and, armed with the 76mm gun, that was only found in a polish unit in NW Europe and, I think one or two British regiments in Italy in 1945.
You can't swap the turret for a 105 because the 105 was not fitted to the M4A1 hull, just the M4 and M4A3 hulls.
In 1943 Canadian units in Italy used the M4 75mm, M4A1 75mm, M4A2 75mm and the M4A4 75mm.
HTH
Paul