I think it is more dependent upon where you live and youand your dialect or Accent; both pronunciations were in use in East London in the 60's [I was there...] and persist to this day.
[I think] sōlʹjər or sōlʹjer is more likely to be heard in places with quite a rapid-fire type of accent, like Newcastle-upon-Tyne or 'Estuary English', as spoken in UK ITV TV'sITV's "The only way is Essex' (TOWIE)
sōldʹyər is more likely in more 'Received Pronunciation' type accents: sōldʹyər, rhymes with "Ok Yar!..."