There are many different ways of making the 'shun' sound at the end of words.
nation magician television
It can be hard to know which suffix to use, but there are rules to help.
If the root word ends in c, then the suffix is usually cian. This is often the case with the jobs people do.
If the root word ends in d, de, s or se, then the suffix is usually sion.
Otherwise the suffix is usually tion.