The home team lost early wickets but recovered to reach 369.
Its first-innings lead of 112 grew another leg with the cheap departure of both Otago openers.
The Volts rallied and were 107 for three at stumps.
But they still trail by five runs and will need to bat for the majority of the final day to get into safe territory.
Dale Phillips has struck rich form late in the season and will resume on 65 with nightwatchman Ben Lockrose yet to score.
Earlier, Canterbury resumed on 153 for two with Chad Bowes on 79 and Jack Boyle on 32.
Boyle was unable to get reset and perished on 43.
He top-edged a pull shot and Leo Carter came and went rapidly.
Otago’s morning got even better when Bowes got himself run out for 100 — his fifth first-class century.
Jarrod McKay struck again for the Volts, nicking out Zak Foulkes for 11.
The Volts had made such headway they may have dared dream of a small first-innings lead.
But keeper Mitchell Hay (62) and Sean Davey (55) put on a critical partnership of 87 from 104 balls for the seventh wicket.
Hay eventually made an error when he sliced a cut shot to Nick Kelly to feed Jake Gibson his third wicket.
But by then the hope bubble had been deflated.
Canterbury had built a useful lead and set about letting more air out of the Volts’ effort.
Spinner Ben Lockrose nabbed the final two wickets to wrap up the innings and restrict the lead to under 120.
McKay and Gibson took three wickets apiece.
The Volts lost opener Mitch Renwick for a duck in the opening over and the captain Hamish Rutherford was trapped in front for 21.
His gesture suggested he disagreed with the decision, but it is in the book as lbw.
Kelly shouldered arms and was bowled late in the day for 20.
The run-fest in Whangarei continued unabated. Central Districts batter Tom Bruce stroked an undefeated 208 and combined in a 218-run stand with Brad Schmulian (98) to help the visiting side post 408 for seven declared.
Northern Districts had put on 496 for six declared and was 25 for one in its second innings at stumps on day three.
