You can replace the capacitor with 0.047 uf 250V AC, class X(2) or Y(2) as Andy says, and that will be just fine.
However the capacitor is only for noise suppression, and this will have no effect on the controller running continuously.
Because the speed must be instantly controllable over a wide range, an AC induction motor would be useless on a sewing machine unless the foot controller was a varispeed inverter : I've never seen one on a sewing machine.
Sewing machine motors are generally "Universal" brushed motors running equally well on AC or DC.
The foot controller invariably turns out to be a combination of a switch (to turn it off at no pressure) and an extremely crude variable resistor, (on Singer machines I've seen from the 1920s to the 1980s; earlier ones didn't need electricity!) by varying the pressure on a pair of carbon (graphite?) rods; the whole lot adjustable for wear by various nuts and bolts. Details differ over the years (decades!) and may include another switch to bypass the resistor for flat out running.
My guess is that some inspection and thought applied to the disassembled foot controller will show what to adjust to allow the switch to open, and give a good range of control speeds.