Holder, 28, was part of the Seattle Seawolves team that claimed the inaugural MLR title in 2018 though he missed out on the final due to injury. The US Army officer is currently part of the World Class Athlete Program at Chula Vista. He is a capped international in both 7s and XVs for the USA.
Adding impressive depth to an already strong front row corps is Waldren. The 27-year-old has returned from a two-year stint with London Scottish in the RFU Championship. He appeared in all five matches for the Eagles in the Americas Rugby Championship, starting against the Argentina XV and Chile.
San Diego are currently in top spot on the MLR table having overtaken the NOLA Gold. They will travel to Toronto on a five-game winning streak.