- Height 6' 0", Weight 225 lb.
- Throws Right, Bats Right
Sierra was signed by scout Hilario Soriano for the Jays in 2005. He began his professional career in 2006, playing for the DSL Blue Jays. That year, he hit .253/.345/.376 with four home runs, 26 RBI and 17 stolen bases (in 20 tries) in 69 games. He played for the GCL Blue Jays in 2007, hitting only .203/.248/.357 with five home runs and 15 RBI. He stole just two bases while being caught twice.
In 2008, he was with the Lansing Lugnuts, with whom he hit .246/.297/.364 with nine home runs, 39 RBI and 12 stolen bases in 23 attempts. He had 11 assists in the outfield but also 10 errors. He split 2009 between the Dunedin Blue Jays (110 G) and New Hampshire Fisher Cats (8 G), hitting a combined .292/.360/.399 with six home runs and 62 RBI. He was named team MVP for Dunedin. In 2010, he only appeared in 20 games, due to two separate stints on the disabled list. For the year, he hit .211/.256/.348 between the GCL Blue Jays and Dunedin.
With the Fisher Cats again and healthy in 2011, Sierra hit .277/.342/.436 with 18 home runs (13 before the break, 5 after), 67 RBIs and 81 runs scored. He had 11 assists and was rated as having the best outfield arm in the Eastern League by Baseball America. He continued to show poor success rates in base-stealing, going 16-for-30. He tied Xavier Avery and Jordany Valdespin for second in the EL in times thrown out running, one behind leader Anthony Gose (who stole 54 more bases). He also tied Chih-Hsien Chiang, Will Middlebrooks and Cody Overbeck for 10th in the EL in dingers. He struggled with the Gigantes del Cibao in the Dominican League that winter, at .217/.295/.283.
He began 2012 with the AAA Las Vegas 51s, hitting .289/.360/.472 with 17 homers (tied for 10th in the Pacific Coast League at the time) in 100 games before being called up to the majors in late July when Toronto traded away Travis Snider. He made his big league debut on July 31st, starting in right field and hitting 9th against the Seattle Mariners. In his first at-bat in the majors, he singled off Jason Vargas and then scored on a Brett Lawrie double. He grounded out and flew out his other two at-bats against Vargas and the Jays lost, 7-2. Sierra hit his first major league homer on August 13th, a solo shot off Jake Peavy of the Chicago White Sox at the Rogers Centre.