The third proven NHL player in the deal is centre Rich Peverley, who also heads to Texas.
The 21-year-old Seguin signed a six-year contract in September 2012 for $34 million US after enjoying a career-best season, but he slumped the past several months. He recorded 16 goals and 16 assists in 48 games, but managed just one goal and seven assists in 22 playoff contests.
Seguin, who can play right wing or centre, was selected with the second overall pick in the 2010 NHL Draft, a pick obtained from Toronto in the trade that saw Phil Kessel head to the Maple Leafs.
Peverley, who turns 31 next week, racked up 12 points in 25 games during Boston's Stanley Cup run two years ago, and followed that effort with 42 points in 57 games in the 2011-12 regular season.
He's been reduced to a more defensive role and managed just eight goals and 12 assists in 68 regular-season and playoff games in 2013.
Eriksson, who turns 28 later this month, also had a dip in production after averaging nearly 29 goals per season over the previous four NHL campaigns. The Gothenburg, Sweden native had 12 goals and 17 assists in 48 games.
He has three years remaining on a deal that represents a salary cap hit of $4.25 million per season.
The right wing, who played in the 2011 NHL All-Star Game, could also help with the development of Carl Soderberg, who Boston plucked from the Swedish Elite League in the spring.
Also heading to Boston: prospects Reilly Smith, Joe Morrow and Matt Fraser.
Morrow had five goals and 14 assists in his first pro season, spent entirely in the AHL. The 20-year-old defenceman from Sherwood Park, Alta., was originally a first-round draft pick of Pittsburgh in 2011.
Smith, a 22-year-old right wing from Toronto, split time between Dallas and their American Hockey League affiliate in his first pro season. He had three goals and six assists in 37 games with Dallas,
The 23-year-old Fraser led the Texas Stars with 33 goals in 62 games, with the six-foot-two left wing offering little production in 12 games with the NHL club. The Red Deer, Alta., native went undrafted during four seasons with Kootenay of the Western Hockey League.
Dallas receives defensive defenceman Ryan Button, a third-round pick in 2009 from Edmonton who has spent two seasons in the minors.