Marchand sent the crowd at La Defense Arena into a frenzy by winning the men's 400m individual medley on Sunday and can expect another red-hot atmosphere when he races in the 200m butterfly and 200m breaststroke finals.
The 22-year-old swam four times across the heats and semi-finals on Tuesday and hopes to have plenty left in the tank.
"It's a lot for my system, so I'm going to have to sleep well, eat a lot, and I'll be ready," vowed Marchand, the poster boy for the Games in the French capital.
US great Katie Ledecky, a seven-time gold medallist, is out to defend her 1500m freestyle title after being relegated to bronze in the 400m behind Ariarne Titmus and Summer McIntosh.
Chinese world record-holder Pan Zhanle is favourite in the men's 100m freestyle final, while 200m freestyle champion Mollie O'Callaghan will be expected to triumph in the women's 100m free.
Japanese gymnast Daiki Hashimoto goes for repeat gold in the men's all-around final, where he is expected to face a ferocious fight from China's Zhang Boheng.
If Hashimoto delivers he will emulate countryman Kohei Uchimura by retaining all-around gold, and keep it in Japanese hands for an unprecedented fourth consecutive Games.
Revenge could be a powerful motivating force for Zhang after China's late collapse in the team final allowed Japan to snatch gold.
In men's basketball, the United States have their sights set on the quarter-finals as they take on Olympic newcomers South Sudan.
Kevin Durant's return from injury inspired the USA to a rout of Nikola Jokic's Serbia in their opening game, an ideal start for the reigning champions eyeing a fifth straight Olympic crown.
"KD was phenomenal," said LeBron James. "It's almost like he never missed anything."
Novak Djokovic, chasing an elusive Olympic tennis gold, meets Germany's Dominik Koepfer in the third round, while Carlos Alcaraz plays Roman Safiullin.
Alcaraz will then return to the court alongside Rafael Nadal in the quarter-finals of the doubles.
In women's football, title-holders Canada must beat Colombia if they are to advance to the quarter-finals following a six-point deduction over a spying scandal.
Canada, who won their first two group games, have appealed to the Court of Arbitration for Sport over the punishment with a verdict expected Wednesday.
The USA are seeking to close out the group stage with a third straight win, against Australia.
Triathlon in doubt
Triathletes face an anxious wait to see if water quality tests allow for their event to go ahead, after the men's race was postponed Tuesday just hours before it was due to get under way in the Seine.
Both the men and women are now scheduled to compete on the same day, but incoming storms could yet scupper those plans.
Heavy downpours overwhelm Paris's underground drains and sewage system, leading to untreated effluent being released into the waterway.
"At this point, we are quite confident that we will have them (races) tomorrow and then we will be very happy all of us, the first ones the athletes," World Triathlon president Marisol Casado said on Tuesday.
If pollution levels remain too high, the triathlon will be turned into a duathlon, meaning only running and cycling.
In other disruption, albeit on the other side of the world, surfing events in Tahiti have been further delayed by unfavourable winds and may not resume until Thursday.
Back in Paris, diving specialists China will seek to continue their dominance in the women's 10-metre synchronised platform, a discipline they have won each time since its inclusion at the 2000 Sydney Olympics.
The first medals in rowing are on offer, in the men's and women's quadruple sculls, while Australia's Jessica Fox has her sights set on another gold in the canoe slalom.
Gold medals are also up for grabs on Wednesday in fencing, judo, shooting, table tennis and BMX.
