Kovalev beat goalie Tim Thomas 4:20 into the second to tie it at 1, and Markov put Montreal up 2-1 moments later when he scored during a delayed penalty call at 5:34.
Plekanec, who scored a hat trick against Boston in a 4-3 win Sunday in Halifax, Nova Scotia, got his fourth goal in two games on a power play at 12:38 to increase the lead to 3-1.
Cristobal Huet made 28 saves for the Canadiens.
Marc Savard assisted on both Bruins goals, including Andrew Ference's on a slap shot from the point with 1:58 remaining in the middle period. Marco Sturm opened the scoring when he redirected Savard's pass beyond Huet for a power-play goal with 1:28 left in the first.