In USA and Canada 240 volt is standard residential voltage in homes.
Residential saunas are 240volt, single phase. Breaker size depends on heater size. Most saunas require a 30 or 40 amp breaker (but may be larger).
Breaker should NOT be GFI type.
Commercial (public) saunas are often 208 volt, 3 phase or other
(If you are putting a sauna in a condo, check to verify voltage.  It may be 208v in a high rise type dwelling; i.e. New York City is mostly 208v)