The Wano Country arc is arguably the greatest story arc in the One Piece series to date, and it has paramount importance in the Yonko Saga. Hyped up to be far superior to what we witnessed in Marineford by Eiichiro Oda, the author of the story, the fans have a rough idea of what to expect from the ongoing arc in the story.
When it comes to Marineford, we witnessed an unprecedented large-scale battle between the Navy and the Whitebeard Pirates, and to best that, Oda will need to go to extremes and introduce a plethora of characters in Wano. With that in mind, here's a list of five characters who we think will show up at Wano, and five who probably won't.
10 Will Appear: Marco
The former First Mate of the Whitebeard Pirates, Marco the Phoenix was sought out by Nekomamushi specifically to aid in the fight against Kaido at Wano. Due to his mind-boggling strength, Marco was described as an irreplaceable asset to the alliance.
Unfortunately, Marco declined the invitation because of Edward Weevil's impending threat. However, soon after, the Marines revoked the Shichibukai system, which put an effective end to Weevil's hunt for Marco for the time being. Consequently, Marco can help out the alliance at Wano by joining the battle, most likely in the third act of the story.
9 Won't Appear: Garp
Garp has achieved legendary status in the world of One Piece, and even though he's just a Vice Admiral, his strength is, at least, equal to that of an Admiral, if not higher. Irrespective of how strong he is, he certainly won't be on the ship to Wano, provided the Navy does decide to intervene in the war.
Garp is a retired officer, and his only job in the organization is to train the young, budding members, such as Coby. He's not an active member anymore, and if a direct war breaks out, Garp is expected to stay put, much as he did at the Paramount War, before the time-skip.
8 Will Appear: Jinbe
Also known as the Knight of the Sea, Jinbe recently joined the Strawhat Pirates, after severing his bonds with the Big Mom Pirates. Jinbe is a veteran pirate, with a bounty of 438 million berries. At Whole Cake Island, Jinbe formed the rear guard, as Luffy sailed off to Wano, promising to join up with them there, later.
It is apparent that Jinbe will be at Wano to help his captain in taking down the sinister Yonko, Kaido. Although he hasn't arrived yet, he is expected to reach the land of Samurai at some point in the third act of the Wano Country arc.
7 Won't Appear: Akainu
Sakazuki, also known as Akainu, is the current Fleet Admiral of the Marines, and undoubtedly, their strongest active member right now. He would certainly be a significant help to the Navy if they were to engage the pirates at Wano.
Even so, the Fleet Admiral never leaves the Marine headquarters, as they usually dispatch their strongest military force, the Admirals, to do the job instead. In case of an all-out war with the Pirates, it is probable that Akainu will send Fujitora, Ryokugyu, and Kizaru, along with the newly formed SSG, to Wano, instead of going there himself.
6 Will Appear: Katakuri
The strongest Sweet Commander of the Big Mom Pirates, and the man with the bounty of 1.057 billion berries, Charlotte Katakuri currently resides at Whole Cake Island. His mother, Charlotte Linlin, is already at Wano with half her crew, and she's formed an alliance with Kaido to take down Strawhat Luffy.
To bolster the alliance with further power, Katakuri could be called upon to join her at Onigashima. However, the event will likely be a predicament for Katakuri, since he noticeably respects Luffy, and wants him to become the Pirate King. Either way, it's only a matter of time before he shows up at Wano Country as well.
5 Won't Appear: Bege
Capone 'Gang' Bege is one of the fiercest pirates on the seas of the Grand Line right now. Taking refuge under the flag of Big Mom, he conspired to murder her during a tea party. Unsurprisingly, his attempt to take the life of a Yonko failed miserably, but luckily for him, he was able to escape safely.
Right now, eight of the eleven supernovas are at Wano, so it wouldn't be out of the ordinary for Bege to be there as well, only, he's at Dressrosa right now, looking for Chiffon. Bege also doesn't have a Vivre Card to Wano, so him being able to make it to the arcane island is nigh impossible.
4 Will Appear: The Admirals
Recognized as the strongest force in the Marines, the current Admirals consist of 'Fujitora' Issho, 'Kizaru' Borsalino, and the mysterious Ryokugyu. Together, they're a threat to any pirate sailing the seas. After hearing the news of Big Mom and Kaido's alliance, the marines have been rattled to their core.
Although action is yet to be taken, their only chance of stopping the alliance is to mobilize the Admirals. Along with the powers of the SSG, the Admirals can possibly make quite an impact on the war of Wano. Undoubtedly, there is a decent chance of them coming to Wano to put an end to the Rocks, once and for all.
3 Won't Appear: Shanks
One of the four emperors who rule the New World, Red-Haired Shanks is a near-imperishable pirate. He possesses a bounty of 4. 0489 billion berries, and his crew is considered to be impenetrable. Shanks arrived at Marineford to end the war and stole the entire show.
While it is possible for Shanks to show up at Wano, it'll be redundant for his character to be used to simply put an end to wars. As a Yonko himself, Shanks has incredible authority, and his appearance in the arc will throw the entire balance into chaos. Unlike at Marineford, Luffy is one of the main contenders in the war, and any intervention from Shanks will lessen the impact of his victory.
2 Will Appear: Blackbeard
The newest of the Yonko, Marshall D. Teach, also known as Blackbeard is growing in both power and authority. In just one year, he has amassed a bounty of 2.247 billion berries, which shows the level of threat he poses to the world. Blackbeard is the ultimate opportunist.
He seized his chance and raided Impel Down when he could, and displayed this side of him again when Whitebeard died, and he took the spoils of war. Blackbeard could make an appearance at Wano Country towards the end of the arc only to steal the devil fruits of the strong people there. Wicked as he is, there's no way he'll let a chance to steal the devil fruits of people like Kaido, and maybe even Big Mom, slip away.
1 Won't Appear: Dracule Mihawk
The strongest swordsman in the world of One Piece, Mihawk, was a member of the Seven Warlords of the sea once. Consequently, he gained the protection of the government, and in return, provided them with assistance against other pirates. Mihawk was called upon when help was needed, like he was at the Paramount War before the time-skip.
Sadly, the Shichibukai system has been abolished now, so if the government does attack Wano, Mihawk won't be there. On his own, Mihawk has no reason to come to Wano, and he already has his handful with the Marines who are trying to hunt him down.