Plante played junior hockey for the Calgary Hitmen of the Western Hockey League (WHL). The Hitmen selected him with their second round pick, 21st overall, in the 2004 WHL Bantam Draft. He established himself as a regular on Calgary's blue line in 2005–06, playing in 54 games. He appeared in 58 more in 2006–07 and attracted greater attention from NHL scouts in the 2007 playoffs, scoring 11 points in 13 games. As a result, the Edmonton Oilers selected him 15th overall in the 2007 NHL Entry Draft, a higher position than he was initially expected to go. Several injuries limited Plante to 36 games in 2007–08 and he failed to report to Calgary's training camp prior to the 2008–09 WHL season, claiming that the team had treated him poorly the previous year. While he initially demanded a trade out of Calgary, Plante ultimately recanted and returned to the Hitmen early in the season. He rebounded from his "nightmare season" in 2007–08 to rank among the leaders of the Hitmen defence with 45 points in the regular season and another 15 in the playoffs before Calgary was upset in the league championship series by the Kelowna Rockets.