McCann was born in Lawton, Oklahoma and attended Putnam City High School, where he lettered in football, basketball and track.
As a senior, he was rated as the 20th-best player in Oklahoma (Rivals.com), but broke his left leg and was only able to play in 3 games, managing to help his team finish a 10–2 season and reach the state quarterfinals.
[1] McCann was an All-Freshman Conference USA selection, after having 38 tackles, 4 passes defensed, one interception and appearing in 11 games, starting three of the last four.
He was the co-winner of the James Bradley "New Mustang" award for consistent play, along with Emmanuel Sanders and Justin Willis.
The next year, he started all 12 games, posting 59 tackles, 7 passes defensed and 4 interceptions, while playing at both corner and safety.
As a junior, he started 11 games, registering 35 tackles, 3 interceptions, one sack and 6 punt returns for 31 yards.
In his second NFL game, he recorded his first career interception on November 14, 2010 against the New York Giants, picking off Eli Manning after Hakeem Nicks stopped short on an intended slant route.
On September 20, 2011, because of injuries to their starting wide receivers, the Cowboys waived him to re-sign Laurent Robinson.