Euchre Call for partner
I have looked but not seen any rules for call your partner games in general where they discuss who wins when multiple people on the same winning hand break the mark for ending the game.

In general when I have been playing we have handled it in the following ways. In a friendly atmosphere it is considered a tie and anyone who hits the mark is considered a winner. In a more competitive atmosphere it is highest score wins. If there is a tie and the bidder is involved in the tie than the bidder wins. If the bidder is not in the tie the win is than considered a tie.

The reasoning for the bidder breaking ties is because they took the action and risk to make the bid. If they are not in the bid it gets a lot harder to determine a tie breaker other than another hand where they are the only ones who can win.