Ok I did a little more looking, you have standard 240v with ground for the larger baseboards and your wiring will most likely be the same as the PNW.
What you will need will be a line voltage smart thermostat. I have no connection with the company, I found MYSA is NRTL listed Similar to UL.
The info I found appears that MYSA will work on 120 or 240v heaters and had lots of good reviews for pairing.
The connections looked similar to your old fashion line voltage thermostats that the black wire is the supply and the red is the switched out , I did not read all the specs but it was common to use 1 thermostat for 2 heaters 240 normally and break 1 leg for each heater or to provide a quick overview
2 heaters fed by 2 wire 240v Breaker #1
1 white to black of stat the stat red wire to heater the black from breaker to the other heater connection connect the ground. Put some black tape on the white conductor coming from the panel.
Now the second heater from another 240v breaker hook up the same on the remaining black red from the thermostat
Remembering to tape the white black. But put the black and white on opposites as breaker #1 #1 or number 1 black on even #2 black on odd to provide 240v for control voltage.
This is how most larger rooms were connected to 1 stat
If you have 3 wire-black, red , white, ground coming from the panel exchange the red will be the second hot (unusual) I believe I have seen 3 or 4 ckts 240v with a neutral these were normally also feeding a bathroom (most bathrooms not all) are 120v
As always make sure my instructions match the oem of the brand you purchase but you want a line voltage smart thermostat I saw some that could gang together but they were not UL listed and most want room thermostats for the control.
One base board use both Hots to both blacks.