the only choice here is connor vs brock
Mayweather vs Big Show worked because it's big show and it doesn't matter if he loses or gives offense to an "outsider". Even though Connor would be far and away the biggest star in the WWE, the weight difference in this match is horrendous and would leave one of them looking like a complete nobody.
If they are gonna have a barely trained Connor at WM, it should be vs a mid-carder who can carry him, and if he's to be involved with main eventers, then have it be a tag match, or he guest referees.