Blair, of Greene County High in Greensboro, played at Appalachian State and was a fifth-round pick in the 2016 draft. He has played in 47 games and made two starts for the 49ers.
Blair, who’s 6-foot-4 and 270 pounds, has 13.5 sacks and 27 quarterback hits in the NFL.
The Falcons problems on defense had a lot to do with porous coverage, according to PFF. The Falcons were ranked 24th in coverage with Desmond Trufant as the only cornerback ranked among the 50 best in coverage in the league.
Alexander, 5-10, 192 pounds, was a second-round pick out of Clemson by the Vikings in 2016. He has played in 55 games and made 10 starts. If he can handle the slot, Kendall Sheffield can move outside and compete with Isaiah Oliver, who struggled in his first year as a starter.
Alexander was PFF’s 17th highest graded cornerback in 2018. He dipped last season, but could be a steal at $4 million a year.
Boston, 6-1 and 205, is a free safety. He was drafted in the fourth-round out of North Carolina by the Panthers in 2014. He’s played in 86 games with 60 starts and has 14 interceptions and 38 pass breakups.
Boston has received strong coverage grades that ranked ninth, 18th and fourth over the past three seasons from PFF.