The 27-year-old Swede has carried the load for the Canucks down the stretch, but with Ryan Miller back from injury there was a chance the veteran netminder could get the call.
Canucks head coach Willie Desjardins played his goalie choice close to the vest this week before confirming Wednesday that Lack will get the nod.
"Eddie's played well in the pressure situations," said the coach. "I'd expect him to be good."
Canucks forward Brad Richardson, who has suited up for just two games since mid-January because of a nagging foot injury, also looks set to play for Vancouver after making it through practices on Monday and Tuesday without a setback.
Meanwhile, Calgary rookie forward Sam Bennett could play his second professional game tonight for the Flames. The 20-year-old picked up an assist in his NHL debut in Calgary's season finale and could draw into the lineup.
"It's definitely exciting," said Bennett. "It's exciting on the ice (and) off the ice. We're all really pumped up for this game and really excited. This will definitely be a fun one."
Second-year forward Sean Monahan said he's good to go for the Flames despite missing practice on Monday and leaving Tuesday's session early.
The Canucks are back in the playoffs after missing out in 2013-14 for the first time in six years, while the Flames qualified for the first time since 2009.
The last three times the teams have met in the post-season (1989, 1994, 2004) the winner has gone on to make the Stanley Cup final.