Emry led Toronto with 72 defensive tackles last season. He also had five tackles for a loss, four pass knockdowns, one forced fumble and one sack over 18 regular-season games.
The six-foot 228-pounder is a seven-year CFL veteran. The Richmond, B.C., native was originally drafted by Montreal with the seventh overall pick in 2008. He spent six seasons with the Alouettes before signing with the Argonauts as a free agent last February.
Emry won the Grey Cup with the Alouettes in 2009 and '10 and was a CFL all-star in 2012.
Foley, meanwhile, is a three-time Grey Cup champion. He was named top Canadian at the 100th Grey Cup in 2012 after helping the Argonauts beat Calgary in the title game at Rogers Centre.
"Ricky Foley has always been an athletic and hardworking football player who continues to produce on the field," Argos general manager Jim Barker said in a release. "He puts tremendous pressure on opposing quarterbacks which is a skill we believe will complement our defence very well.
"Ricky has won championships on every team for which he has played in this league, and many of our fans will remember him to be a key contributor to our 100th Grey Cup win. Toronto is his hometown and we are happy to have him back in Double Blue."
Foley, from Courtice, Ont., also won championships with the B.C. Lions in 2006 and Roughriders in 2013. He had 54 tackles, 12 sacks and one fumble recovery for Saskatchewan last season.
The nine-year veteran was drafted by the Lions with the fourth overall pick in 2006. The six-foot-three 256-pounder was named top Canadian in the CFL in 2009.