Loewen grew up in Surrey, British Columbia, and was both a starting pitcher and first baseman for the team that represented Canada at the 1996 Little League World Series in Williamsport, Pennsylvania. He would go on to attend Fraser Valley Christian High School and play baseball for the Whalley Chiefs of the British Columbia Premier Baseball League. While playing for the Chiefs, Loewen was selected with the No. 4 overall pick of the 2002 Major League Baseball Draft by the Baltimore Orioles. As of 2008, this is the highest a Canadian player has ever been drafted.