Correct sentences

[Saladin]

Please can you tell me which sentence is the correct one or are they all correct? sometimes i do confuse about could and would.

Even if i come to Sweden what could i do for you?
Even if i come to Sweden what would i do for you?
Even if i come to Sweden what can i do for you?

thank you very much

[Tdol]

Even if I come to Sweden, what can I do for you?
This is the natural first conditional sentence.

Even if I come to Sweden, what could I do for you?
This is possible; you can use 'could' in a first conditional, if trying to be polite, for example.

Even if I come to Sweden, what would I do for you?
Some would say this is wrong and that you should use 'came' with 'would' to make a second conditional. Indeed, it would generally be marked wrong in tests and exams. It might be possible, if 'would' were used for politeness, but I would avoid it to be honest.