One common theme is the other nations' concern or lack thereof. Since Canada is often overlooked, sometimes the other characters are slow to realize he's sick. Another theme is Canada's own struggle with his illness in solitude. He might be used to taking care of himself and not wanting to bother others.
I'm not sure of a specific 'Hetalia Canada sick fanfiction' title off the top of my head. But you can start your search by looking at fan - created reading lists. These are often compiled by die - hard Hetalia fans who have a passion for collecting different types of fanfictions. They might have a section dedicated to stories where Canada is sick. Another way is to search on Wattpad, though the Archive of Our Own has a larger and more organized collection of Hetalia fanfictions in general.
He would probably be very polite. Canada is often depicted as a polite nation, and this would likely carry over to his human form. He might be a bit shy, too, since he sometimes gets overlooked in the Hetalia series. Also, he would be very knowledgeable about nature and the outdoors, given Canada's vast and beautiful landscapes.
Well, it could be a story where Canada turns into a girl due to some magical or mysterious event. As a girl, she discovers new aspects of her personality. She might become more assertive or more in touch with her emotions. And in terms of her relationships with the other Hetalia characters, she could form new friendships or rivalries. For instance, she might have a rivalry with France who is always a bit of a flirt and now sees her as a new target for his charm.
Another storyline might involve a friendship that develops during a global event in the Hetalia universe. Let's say there's a big international sports competition. The OC, who is a huge sports fan, teams up with Canada to support their respective countries. Along the way, they face challenges like dealing with over - competitive nations and learn about each other's values and traditions related to sports.
Perhaps there's a treasure hunt involved. The pirates believe America has some clue to a great treasure because of his unique position in the world. So they take him along on their adventure, and along the way, there are lots of comical misunderstandings as America tries to explain modern concepts to the pirates.
America has a lot of cultural influence in the real world, and this is often translated into the Hetalia universe. His pop culture, such as movies, music, and fast food, are things that could potentially draw other characters towards him. In fanfiction, this can be shown as the other characters having a fascination or love for America because of these aspects.
One great fanfiction could be 'The Pirate's Treasure'. In it, Pirate England and America go on an adventure to find a hidden treasure. It has a lot of action scenes and also some interesting character interactions. For example, their banter while on the ship is really engaging.
A political intrigue plotline could also be fascinating. Maybe there's a situation where they have to work together to solve an international crisis, but there are other countries trying to undermine their efforts. It would involve a lot of strategy and diplomatic maneuvering between the two characters, with some tense moments and perhaps a budding respect for each other's abilities.