If you want mechanical cantilever brakes with a GRX crank and derailleurs you can use mechanical brake road shifters.
Tiagra 4700 series shifters are compatible with with 10 speed GRX
105 (5800 and 7000 series) and Ultegra (6800 and 8000 series) shifters are compatible with 11 speed GRX.
You also have the option of using mini v-brakes with road shifters as these match the cable pull of the brake levers in the shifters. Note regular MTB v-brakes should not be used with road brake levers as they use a different cable pull.