Here is the full list of Super Bowl/Grey Cup dual winners (12 in total) as far as I have researched it (accurate to 2015, not aware of any others since then, but not confirmed):
NOTE: Super Bowl year refers to the NFL season played, not the actual calendar year of the game itself (so a team listed as winning in 1987 actually won the Super Bowl game in January 1988)
OJ Brigance: GC - Baltimore 1995, SB - Baltimore 2001 (only player to win both playing for the same city)
Brandon Browner: GC - Calgary 2008, SB - Seattle 2013 (did not play in game, suspended) and New England 2014
Dan Federkeil: SB - Indianapolis 2006, GC - Calgary 2014
Terry Greer: GC - Toronto 1983, SB - San Francisco 1989 and 1990
Harald Hasselbach: GC - Calgary 1992, SB - Denver 1997 and 1998
Tim Jessie: SB - Washington 1987, GC - Winnipeg 1988 (as noted, only player to win both in the same calendar year)
Josh Miller: GC - Baltimore 1995, SB - New England 2005 (greatest gap between championships)
Andre Rison: SB - Green Bay 1996, GC - Toronto 2004
Bobby Singh: SB - St. Louis 1999, GC - BC 2006 (also won an XFL title with LA in 2001, the only player to pull off the NFL/CFL/XFL trifecta)
Alvin Walton: SB - Washington 1987 and 1991, GC - Baltimore 1995
Barry Wilburn: SB - Washington 1987, GC - BC 1994
Tyrone Williams: SB - Dallas 1992 (practice roster player only) and 1993 (roster but did not play in SB game itself), GC - Toronto 1996
Two other fun bits of trivia:
Yo Murphy won a World Bowl title with Scotland in 1996 (was the game MVP to boot), won a Grey Cup with BC in 1994 and with Saskatchewan in 2007, and lost the Super Bowl with St. Louis in 2001 (and played in the XFL as well, only player to start in all 4 leagues and play in the WLAF/NFL/CFL title games)
Jackson Jeffcoat won the Grey Cup with Winnipeg in 2019, and does not have a Super Bowl ring but could easily inherit a pair. His dad Jim won 2 titles as a player with Dallas in 1992 and 1993.