Bergevin and the Canadiens acquired Kassian from the Vancouver Canucks in exchange for Brandon Prust and a 2016 fifth-round draft pick on Wednesday.
"We're bringing in a younger player with a big body who's a bigger offensive threat," said Bergevin at a press conference on Thursday. "We're aware his consistency is not quite there, but that's the case with a lot of young players.
"If he reaches his potential, we have something good for a long time."
The 24-year-old Kassian had 10 goals and six assists in 42 games with the Canucks last year, missing a chunk of the season with a back and finger injury. The six-foot-three forward has 35 goals and 31 assists in 198 career games.
It's the second NHL trade for Kassian, who went from Buffalo to Vancouver in 2012. The physical right winger, who was selected in the first round of the 2009 draft by the Sabres, is good on the puck and could evolve into a top-6 forward for the Canadiens.
The native of Windsor, Ont., had 81 penalty minutes with Vancouver last year and 124 the year before.
"I'm looking for a fresh start," said Kassian on a conference call on Thursday. "I couldn't be more happy — an original-six team with the best fans in the league. I consider myself lucky to be here.
"Montreal's a good, deep team. Any way I can fit in to help the team, I'll strive in that role and try to make the team better."
Shortly after the trade was announced, Canucks forward Alex Burrows, Kassian's former teammate, said the move was risky because Kassian had "bumps" on his lower back.
Bergevin, however, was not overly concerned by Kassian's prior injury troubles.
"Before making the trade, we looked at his medical records," said Bergevin. "It's nothing structural. Players always get injured, but there was nothing alarming in this case."
The trade gives Bergevin and the Canadiens additional cap space.
Kassian has a year left on his contract at a cap hit of US$1.75 million. Prust, on the other hand, would have cost Montreal $2.5 million of cap space.
Bergevin also saved some cap space by buying out forward Pierre-Alexandre Parenteau's contract on Monday.
That money may go towards a contract extension for Alex Galchenyuk, which is currently in the works. Bergevin could also acquire a big-name player such as Eric Staal.
On Thursday, the Canadiens GM was less than candid about his plans.
"I always think it's interesting to have a little cushion," said Bergevin. "I have money. I don't have to spend it. But I'm always looking. Part of my job is always to make my team better."
In addition to trading Prust for Kassian, the Habs general manager made other moves this week.
Montreal offered contract extensions to defenceman Greg Pateryn (two-year extension), forward Brian Flynn (two-year) and forward Christian Thomas (one-year).
The Canadiens also offered a one-year, two-way contract to defenceman Mark Barberio. A native Montrealer, Barberio played 103 career NHL games with the Tampa Bay Lightning.
Notes: The Canadiens' annual development camp begins Sunday. A total of 43 players will take part in the four-day camp.