#3 Rusev
Although Rusev probably wouldn't have much use in this match , especially with how the WWE is booking him right now, he would be a warm body for the company to replace Mustafa Al with. It could also help further his storyline with Shinsuke Nakamura, and maybe even keep the WWE Universe on its toes.
Think about it! If Rusev ends up in the match, all WWE has to do is have Nakamura come out and attack several superstars to create an unbelievable WWE moment. Beyond that, it also would create a reasonable doubt as to whether Bryan could retain or not, which is something the WWE title picture desperately needs right now.
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In the end, Rusev isn't the best choice to fill this spot, but it would be a way to further his storyline with Nakamura, while also creating doubt as to whether Bryan comes out on top. This scenario allows for the company to do both of these things and kind of creates an 'OMG moment' in the meantime.