wish and hope both express the emotional attitude of the speaker- a desire for something. wish can have overtones of sadness or disappointment- you expect not to get something, whereas hope expresses optimism- you do expect to get something, usually with reason.
can and could both indicate the real situation, or the speaker's rational assessment of it. can is used about something that is possible: could is used about that is improbable.
Using the combinations hope/can and wish/could reinforces the message.
I hope I can visit all the countries in the world one day.
This expresses an optimistic desire to visit all countries, backed up by a rational belief that this will be possible.
I wish I could visit all countries in the world.
This expresses sadness: a longing to do something that the speaker rationally considers to be impossible. Note that, because the speaker considers it impossible, they would not finish it off with one day.
To address your question: these are two standard forms that carry the right emotional and rational overtones for most situations, but neither really fits the bill for your situation. If you could combine hope with could, this might convey the right meaning, but this combination is never used about future events. You will therefore have to spell out exactly what your emotional and rational additude is:
I hope to visit all the countries in the world one day, but I know that it's going to be difficult.