The only way to have online mutliplayer and interaction in general on the Wii right now is if one were to hack the Wii system, usually using the Homebrew setup. I personally don't know how to hack my and due to the fact that it has now been replaced by my Wii U (while also having my GameCube nearby to still play Melee), I can only offer so much information about hacking a Wii system. I'm sure if you search on how to hack a Wii system to gain online features again via YouTube videos or site links, you will be able to have the features on your Wii (and Nintendo DS systems to a further extent if you want) to your liking.