For a fiction based in real history, Vinland Saga has done an amazing work making characters interesting no matter if they are historic figures or entirely fictional creations. Even focusing just in the bits of story which have been told in the anime, a good number of charismatic characters have earned the fans' admiration. In Canute's case is the first option, but thanks to his surprising character development, even if you knew he would eventually become king.
The Life Of Royalty
Canute was born as the youngest son of King Sweyn of Denmark in the year 996. His father was always driven by the Viking spirit, the glory of war and the value of a great warrior. During his regin he managed to conquer almost the entirety of England. As such, he valued and loved Canute's brother Harald, also an army commander and hardened by countless battles.
Canute on the other hand showed to have a greatly different personality from early on. Basically raised by Ragnar, his chief retainer, he became a devoted Christian and hiding behind Ragnar's overprotective attitude he turned shy and secured. He developed interests far from the war and the common traditions of a warrior-oriented society, like cooking, something he loved and worked on, but that was deemed by his own father as "slave work" and unworthy for a prince.
As time passed he got more distant from the politics side of royalty and secluded in his own little world alongside Ragnar where the preoccupations went as far as the taste of their last meal. Sweyn was well aware of Canute's path which angered him. He saw his son as a weakling, someone who would never carry the weight of the crown. His looks didn't help his case either, as Canute's effeminate face and long blond hair often got him mistaken for a girl, to the point of being considered the reincarnation of the goddess Freyja.
Sent To The Battlefront
Late in his life King Sweyn started to think about succession, maybe stepping down for a few pleasant years before death or just having the assurance that upon his death the kingdom would be in good hands. He was aware that some nobles were picking sides between Canute and Harald to gain political power if their candidate ended up becoming king. To avoid any kind of conflict, he plotted to kill his own son Canute, so Harald could be the undisputed heir to the crown.
Sweyn was a great battle strategist, and knew that the chances to successfully take over London were low. He sent Canute to the battlefront in London, hoping he would end up killed by the enemy. At this point Canute was just a teenager with a body and personality poorly suited for war. It was evident for Ragnar that the king was trying to get him out of the way. However, this only led to Ragnar being even more protective with him, and as Askeladd realized later, get in the way of Canute's emotional maturity.
Against Sweyn's will, Canute was held hostage by Thorkell when they lost the battle of London. He wanted to use him for a negotiation, without knowing he was of no value to the king. From the hands of Thorkell he was rescued by Askeladd's group. He didn't want him for negotiation, but for political leverage. He wanted to turn him into the next King, and playing the part of his counselor, influence his decisions. Up to this point, Canute is nothing more than puppet, moved around for the personal interest of others.
Sudden Change And New Goal
Spending time with the Askeladd-lead mercenaries, Canute had a time to discover himself. First his relationship with Thorfinn, someone consumed by hatred and with an entirely opposite attitude towards him in comparison to what a prince is used to. He was put in positions where he had to show his face and speak up, and it wasn't by accident. Askeladd wanted him to change, and he forced those situations time and time again, and after seeing how he was so dependent on Ragnar, hiding behind him at any chance, the ground was settled for the next move.
Askeladd managed to murder Ragnar during a fight, thinking this will give Canute the chance to be himself for the first time.The time of revelation comes when Askeladd's troops betray him, afraid that his luck ran out and seeing that Thorkell is about to catch them. They tried to capture Canute, but with some help they try to scape. However, his ride breaks down. The prince finds himself laying down in the snow, deep in thought, as he has been ever since Ragnar died.
His hatred of war makes him wonder why everyone keeps fighting and dying, as the screams of the ongoing battle reach him. He can't understand what was so wrong with Ragnar raising like a farmer would with his child. He despises royalty and wishes to have been born far from it. However, after he wakes up, his conversation with the monk makes him realize not only the true meaning of Ragnar's feelings, but his mission in the world.
True love only exists in God's work, but not in the human heart. To solve the original sin that provoked this situation, Canute entrusts himself the mission to create paradise on Earth. There's no point in waiting or looking for salvation. In order to obtain that better world, to help create this true love within people, you have to destroy the foundations of the current society. And to do so, the first thing he had to break was himself.