Install Smart Switch - Neutral wire from adjacent switch?
Looks like your switch is at the end of the line loop. That is why you have neutral and black joining in the switch. This is a case where power goes into light first, and then the switch.
Possible case: https://www.buildmyowncabin.com/electrical/wiring-switch-power-into-light.html



For multiple switches, the neutrals are joined together, and that is what you see in the other 3-way using a "marrette" (I had to look this word up)
https://www.buildmyowncabin.com/electrical/wiring-diagram-multiple-lights-multiple-switches.html


I think you can control by joining with the neutral from other switch (As long as you are sure that it is indeed the neutral).
Put the white of current switch into your smart switch live. The black wire going into old switch into smart switch load. Neutral from other switch will go into neutral of smart switch too.

There should have been a black tape on the old switch's white wire. Not sure, it might be just the code requirement in some states (maybe also in Canada). You can add it now anyway.