There was little riding on the contest with both teams out of finals reckoning but Marr (16 points) and Arthur Szwarc's 11 points fuelled Canada to a 3-0 (25-21, 25-23, 25-22) triumph to end a three-match losing streak.
A slumping Canada endured a straight-sets defeat to Serbia on Friday to end their faint hopes for next month's finals in Lille but they overwhelmed China through firepower despite resting numerous mainstay players. China were looking to continue a successful home stand after beating Japan on Friday but an error-prone performance marred their effort and they slumped to a disappointing 3-11 overall record.
Canada have now won their past six matches over China at the major world level and this result was never in doubt despite Jiang Chuan's (12 points) best efforts. With both teams playing freely, the play was marked by long rallies, desperate defending and some blistering blows as points were traded early.
Canada's firepower was evident with China libero Tong Jiahua constantly under pressure but he was doing well to repel the attacks as the hosts held an 8-5 edge at the first technical timeout. Canada muscled their way back into the contest with Szwarc imposing his will as China's precocious teenager Zhang Jingyin struggled under the pressure and he was soon substituted out of the contest.
China were gifting points away and Jay Blankenau's mastery at the net ensured the visitors dictated terms. The hosts clawed back within two late in the set as the rowdy crowd intensified but Marr stepped up with timely plays to ensure Canada took an early lead.
Marr continued to menace in the second set as a precise Canada was executing their sets to perfection to continually befuddle China. Chuan was working on overdrive to keep China afloat but the hosts were stymied by Canada's imposing frontline.
China were being undisciplined at the net as the match appeared to be slipping away with Blankenau's cunning swerve and Marr's spectacular aerial prowess ensuring Canada pulled away. Libin Liu answered with swirling swerving to eat into the deficit and soon enough China hit the front at 18-17 before undoing their good work with a slew of unforced errors.
Canada claimed a pulsating rally - which had spectators notably gasping - through a Marr spike to lead 24-21 and he soon sealed the deal to ensure his team gained a stranglehold of the match.
Canada were keen to wrap up the match quickly and ensure the crowd did not awake as they started the third set quickly with the first five points punctuated by a booming kill from Szwarc. China inched back but Lucas Van Berkel stymied the attacks with booming blocks along with determined libero Bryan Duquette, whose play was marked by full-length dives.
As had been the case all match, an error-strewn China made crucial service errors as Nicholas Hoag produced the winning spike to ensure Canada moved to an overall record of 7-7.
Canada finishes their campaign against Japan on Sunday, while China plays finals-bound Serbia.