Without your circuit and the type of analysis, the answer is not precise. In short, it seems you need variable from an external file instead of being generated by QSPICE. It really depends on whether your Monte Carlo values need to be fed into pre-processed data or not (for example, value in V-source and generic SPICE devices normally requires pre-processed data, where the value must present before simulation starts. But B-source can accept post value, that why it accpet node voltage like V(x) in its formula.)
If you must feed a variable (parameter) to a V-source, you may have to consider chaning netlist value in each simulation run and can be done with external program like Python using batch commands. The idea is to repeat the simulation with the netlist modified with your Monte Carlo values. Possibly the work of @masashi.nogawa can help.
https://forum.qorvo.com/t/pyqspice-a-python-scripting-interface-for-qspice/15723/19
If you are allowed to feed a variable to a B-source, you have the option to load parameters by using a custom DLL-block to read an external file and feed the value into the simulation. Results would look like this.
