Edmonton leads in the standings with 10 points and a 3-1 record. Quebec's LHFDQ Nord follows with nine points having defeated North Bay 3-1 earlier in the day.
The Thunder came back from a 4-1 deficit early in the second period by scoring once in the second, twice in the third to send the game into overtime.
Alexandra Poznikoff opened scoring for Edmonton in the first and tied the game sending it into overtime with just 25 seconds remaining.
Boucher also scored Edmonton’s lone second period goal and made it 4-3 late in the third.
Regina’s Teah Anderson scored twice for Regina while singles were scored my Morgan Casson and Andie Wilyman.
Earlier Wednesday, Eve-Audrey Picard had a hat trick in the third period to power Quebec past North Bay.
The Ice Boltz goal came from Taylor Murphy late in the second period.
In the late game, Delaney Duchek scored a tiebreaking goal in the third period to give Atlantic Champions Metro Boston Pizza their first win of the tournament, 2-1 over the winless host team Fraser Valley Phantom.
Following Thursday’s final robin play, semifinals will take place Friday with the bronze and gold medal games being played Saturday.