ORLANDO — Earlier this summer, former Giants catcher Andrew Susac came out to a game at Oracle Park and caught up with the man he backed up for a couple of seasons. When Susac returns to San Francisco next season, it’ll be for a much different reason. The Giants on Wednesday traded for Daniel Susac, the younger brother of Andrew, who was Buster Posey’s backup in 2014 and 2015. Daniel Susac, 24, is a former first-round pick who was left unprotected by the Athletics ahead of the Rule 5 Draft. He was taken fourth overall by the Minnesota Twins and then sent to the Giants, who had tried to acquire him from the A’s earlier this offseason. As a Rule 5 pick, Susac must stay on the roster the entire season or else he must be placed on waivers and then offered back to their original team. That designation, plus the fact that the Giants gave up minor-league catcher Miguel Caraballo and cash considerations for him, makes him the early frontrunner to be Patrick Bailey’s backup on Opening Day. “I think he’s a candidate,” general manager Zack Minasian. “Obviously he’s going to have to come in and earn it, but obviously...