So in that configuration you have a single switch with three rockers, each of which sends a switched hot for each of the three functions, fan, heater and light.
While you could swap out the switch box for a three gang and add 3 smart switches for each of the functions, you’d have to pay special attention to the heater switch. The heater draws 1500W (12.5A), which is considerable. You’d need a smart switch that can handle that load, or you can use a dumb switch there. The Gen 2 Inovellli switch would probably work hear, as well as the upcoming Project Vernacular switch.
As an alternative, you could use a single smart switch with no load. You’d need a smart relay with three channels (Zen16, maybe) mounted up at the fan. You would send an unswitched hot and neutral from the switch box to the fan and use the relay to turn the three functions on and off. The relay would be controlled using automations spawned from multi-taps on the switch. Since the switch wouldn’t have a load, and smart switch capabable of sending scene commands would work.