Microshift makes an 11-speed flat bar road shifter set. Looks like it runs around $75
https://www.amazon.com/Microshift-speed-flat-road-shifters/dp/B011F8X8KE

I used the Microshift 10 speed version of these for a flat bar conversion for my wife. They work great.

Shimano makes some flat bar road brake levers (which are basically canti levers) for pretty cheap.

Don’t worry about them not mounting on the same clamp. Many flat bar bikes have the brakes and shifters with separate clamps.