You can go here and calculate the servo torque you'll need.
Servo Torque
Sig recommends "heavy duty servos" (whatever that means) for their 1/4 scale Cub. I'd see what the calculator has to say but something in the 75 ounce plus torque range will probably be fine. Depending too if you're doubling up anywhere like one for each aileron, etc. But why stop there? You can get some pretty powerful servos today for near pennies.
Servo City is a good source for checking specs on a lot of servos at once.
Servo City
Last but not least, I'm working up a Hostetler Piper Cherokee. 108 inch wing. Here's what I worked up for the servos:
Aileron - 100 oz x 2
Flaps - 200 oz x 2
Rudder - 50 oz x 1
Flying Stab - 150 oz x 1
The calculated torque is far less than what I elected to go with. Example: The flaps at 40 degrees deflection calculated to 147 oz at 85 MPH. I don't think this model will do 85 MPH without the help of gravity. And I doubt I'll ever try to deploy flaps at full speed. The ailerons at 30 degrees deflection (that's a lot) calculate to 50 oz at 85 mph.
So try the calculator. It was a learning experience for me. You'll need the dimensions of your control surfaces. Difficult on the tail surfaces but a good estimate will work. The area of the surface is what you're after.