It ís possible to shoot with cant, as yr shooting at a fixed distance; 10m. Its hard however, to always have the same amount of cant. Its kinda logic that correcting that causes more problems, cause corecting means muscle strain which means flyers.
Dont think the cant is caused my muscles, unless it ónly occurs after prolonged shooting.
Yr cant is probably caused by a fault in yr stance. Might be yr zeroposition.
Might be the way you grip the pistol, might be yr left eye dominant but shooting r/h. If you hold the pistol in front of you, just like when shooting, and you close yr eyes a sec, than reopen, the front and rear sight should still be aligned. Both horizontally and vertically. If its nót, than yr grip is wrong; that is, either the wáy you grip it, or the grip itself doesnt suit you.
I'd say, try getting back to basics, and try fixing yr grip and stance fírst.
Dont think the old Steyr have sideways grip cant adjustment by the way.