Adrian Gonzalez, first baseman of the Boston Red Sox was awarded the title of cover athlete after he batted .338 with 27 home runs and 117 runs batted in during the 2011 season. Gonzalez is the third Red Sox player to be awarded the cover, the first being David Ortiz for MLB 06: The Show, and the second being Dustin Pedroia for MLB 09: The Show.
On January 23, 2012, it was reported that there will be a separate cover for Canadian buyers, with Toronto Blue Jays right fielder/third baseman Jose Bautista on the cover. Bautista batted .302 with 43 home runs and 102 runs batted in during the 2011 season.
Source: Wikipedia, "MLB 12: The Show", available under the CC-BY-SA License.