In spite of his struggles against Thanos, the Hulk is still considered the strongest hero there is in the Marvel Cinematic Universe, remaining the Avengers' preeminent tank. The closest thing the cinematic X-Men have to match the Hulk's strength is Colossus. In the comics, Colossus is strong but not on the Hulk's level. However, the two's most recent cinematic incarnations might just prove that, if the two went head-to-head, Colossus would obliterate Hulk.
MCU Hulk is WAY Stronger Than Deadpool's Colossus
The Hulk has been the Avengers' powerhouse since the Battle of New York. While it feels like he's spent as much time fighting his teammates as he has super villains, he's played an integral part in defeating Loki and Ultron.
During the events of Thor: Ragnarok, he became the top gladiator in the Grandmaster's Contest of Champions. After leaving the fight game behind to team up with Thor and Valkyrie, the Hulk would go on to single-handedly defeat the Fenris wolf, allowing his teammates to evacuate their kingdom.
Colossus is Weaker but a MUCH Better Fighter
While Colossus isn't the force of nature Hulk is, he does outclass the Jade Giant in some ways. Most prominently, he's a much better team player. While his relationship with Black Widow made him less volatile, the Hulk was always more of a weapon than a teammate.
Colossus poses no such problem for the X-Men. He's always up for lending his allies a hand, even to Deadpool. Unlike the Hulk, he can use his powers defensively, like when he used his armor to block gunfire from Stryker's troops in X2.
He also knows how to use his powers in tandem with his teammates. Whether it's sharing them with Rogue so she can shield herself from shrapnel or setting up Wolverine for a Fastball Special, Colossus can use his powers to make those around him better.
The MCU's Hulk Is Also Immortal
A dark yet comedic scene in Thor: Ragnarok proves Bruce Banner's immortality. Bruce leaps out of a ship, expecting to hit the ground as the Hulk (like he did in his 2008 solo film). Instead, he crashes into Asgard's Rainbow Bridge as Banner, his body broken and surely on the brink of death.
The Hulk eventually joins the battle, showing that he has a similar relationship to Banner in the MCU as he does in the comics. The Hulk's ability to overcome any trauma that happens to him or Banner makes him functionally immortal. While he can be beaten savagely, as Thanos did in Infinity War, it doesn't appear that the Hulk can be killed by physical means.
On the other hand, the cinematic incarnation of Colossus is mortal. He fell to Sentinels twice in the dystopian future of X-Men: Days of Future Past. His first death came when his head was caved in after losing an arm by an adaptable Sentinel that mimicked his powers. Kitty Pryde and Bishop were able to change the past so that didn't happen. When the surviving X-Men were buying time for Wolverine as he attempted to change the past, Colossus was torn in half while in his armored form.
Colossus Defeated The Juggernaut
Colossus was always part of a large ensemble in the X-Men films, but took on a bigger role in the two Deadpool films. In the first film, he aided the Merc With a Mouth by fighting Angel Dust, allowing Deadpool to focus on rescuing his girlfriend Vanessa.
Colossus's most impressive fight in the Deadpool series — and his cinematic history in general — was against the X-Men's most "unstoppable" foes. He didn't just stand toe-to-toe with the Juggernaut either — he defeated him.
It is true that Negasonic Teenage Warhead dealt the final blow to Juggernaut. Her girlfriend Yukio also provided an assist, keeping Colossus from potentially being impaled. However, Colossus is the one who did the lion's share of the work. His quick thinking caused Juggernaut's fall into a pool to be a potentially fatal one, as he was electrocuted by a cable Colossus shoved into a vulnerable part of Juggy's anatomy.
Colossus would be a formidable opponent for the Hulk at full strength, especially with the burgeoning mean streak he's picked up from working with Deadpool. The incarnation of the Hulk last seen in Endgame might have real trouble with him.
Professor Hulk is a more well-adjusted character, but he's also one who's been weakened by his battles with Thanos and the loss of his comrades. If Marvel Studios decides to introduce the X-Men to the MCU with an Avengers vs. X-Men adaptation, we might see Colossus slay another giant.