Can they work together? Can Bossk change a critical into 2 hits then change all other criticals to hits with the Heave Laser Cannon rule. As per the rule of resolving in The order you see fit?
Bossk and Heavy Laser Cannon
No.
HLC's effect works immediately after you roll dice, before you enter the 'modify attack dice' step.
Bossk's ability happens AFTER all dice modification and AFTER all the results have been compared. Only then can he cancel a kaboom and add two booms.
However, note that any crits which come up as part of modifying your HLC roll (e.g. rerolls from Target Lock, Predator, Dengar, the EPT Calculation, etc) remain crits.