Do you think Cardano will replace Ethereum?
Personally, I think that both blockchains will develop in different directions in the future.
Both blockchains would therefore be relevant and coexist.
I personally think of something like this:
Ethereum = DeFi
Cardano = dApp
I also thought of something like this:
Ethereum = NFT & Gaming
Cardano = dApp & DeFi
As other have said, Cardano is no way going to replace ETH. Ethereum is considered to be a prime mover, and even during it's early stages in 2017, there are a lot of projects that challenges it to the top if I remember correctly, and most of them are dead projects now, meaning they didn't succeed during that time although there are a lot of hype on this projects. So this could be the case again for those who want to challenge Ethereum, like ADA as per OP or Solana which is very hype right now. But if you like to go for a win-win here then just invest on both and don't compare their technology. For sure you are not looking for the technology behind isn't it? But how you can take advantage or this project and make money specially that the bull run is going to come.