Difference in starting pronunciations of "station" and "sun"

If you look up the official pronunciation of 'sun' and 'station' you get respectively

• sun - /sʌn/
• station - /ˈsteɪʃən/

with no notated difference. No standard or dialectal variety of English has any difference either.

But it is the case in many foreign languages that they do not allow the complicated consonant cluster of /s/ followed by a harder consonant, or some change is needed to the /s/. Then this gives a sound change when they try to speak English.

This is especially true of Spanish where there are many close cognate words or borrowings from the same source (Latin). For example:

school (En) - escuela (Sp)

This is a pattern for 's' followed by 't', 'p', or 'k'. There is a tendency for native Spanish speakers to naturally say the English word 'school' as 'ehs-kool', which is closer to their own native pronunciation.

In Japanese, because any consonant pair is forbidden, they tend to put a vowel -between- an English word that has two consonants 'suh- koo -luh' (and a vowel at the end.

So I suspect that the 'estation' pronunciation that you are hearing is from a non-native speaker of English that speaks a native lanaguage that treats 'st' differently than English. No native variety of English has a difference between 'sun' and 'station' for 's'.

The 't' in 'station' is a whole nother story.

The only people who pronounce station (or scale or school) with a leading e sound before the s are those who cannot pronounce a “liquid s”; that is, native Spanish speakers.

Which is why they say estación ( and escala and escuela), at least when speaking Spanish.

Because of this, sometimes when native Spanish (or Portuguese) speakers speak English, they introduce an epenthetic e at the front of words beginning with an s that is followed by a consonant. They do this so they can split up the consonant cluster, placing the s at the end of a new first syllable, and the other consonant at the start of the next one.

They also do this when borrowing English words into Spanish. So English stress becomes Spanish estrés, just as English standard becomes Spanish estándar. Notice they drop the d at the end, because they can’t say an rd at the end. They can’t say most consonants at the end of a syllable, actually. That’s why when they say the borrowed word stop, this comes out sounding like estó, estod (IPA /esˈtoð/), or estoz (IPA /esˈtoθ/) — and sometimes even estof. Since they can’t have a final p either, they have to substitute in something that works for them.

It may be that native speakers of other languages also introduce an epenthetic s at the front of English station. However, this is not a standard pronunciation, and would mark you for a non-native speaker.

Station doesn't begin with an “e” sound, it starts with an “s” sound, just like sun.

Here's how the Oxford English Dictionary says they should be pronounced:

/ˈsteɪʃən/

st - ay - sh - ə - n
IPA   Sounds like

• st      st    as in stay, post (main stress)
• eɪ      ay    as in bay
• ʃ     sh    as in shop, dish
• ə     ə    as in another (schwa)
• n     n    as in nine
  

/sʌn/

s - u - n

IPA    Sounds like

• s      s    as in see
• ʌ      u    as in butter, upset
• n       n    as in nine

Although note the ˈ mark in /ˈsteɪʃən/ and not in /sʌn/. This symbol is placed before the stressed syllable.