Do higher level users have a higher chance to win than low ranked users in a single giveaway?

No. Assuming they are in the same giveaway.

Yes.

Higher level users can join higher level giveaways, with much less number of average entries, so practically speaking - yes, there's a much bigger chance to win let's say L2+ giveaway rather than L0.

Theoretically speaking, your chance for winning is always 1 / numberOfEntries.

Everyone has an equal chance as long as they can enter in the giveaway.

Everyone has same chance but users who are higher levels get into giveaways that have less people so they are more likely to win games.

I'm level 6, can I have a game?

No! ;)