Omg! I also shipped france with canada! but i'm relieved to know the ship isn't popular considering the hate it'd get especially when france did raised canada. I know there could be elements that is somewhat problematic. But I really enjoy headcannons that france is such a good dad on matthew and that's all i need to know. I feel like the age argument could be argued to a lot of ships to be honest, like japan x china, while a niche ship, could still be applied since china, in a way, raised japan.
Now, I'm thinking about the age gaps and ships in hetalia.
But anyways, I could never understand as to how prussia x canada came to be and went to become as one of the popular ship in the fandom. I was unaware of its conception so i don't really have an opinion other than confusion.
And i know right, roddy and gilbert had something going on that made me see them as a ship potential. their supposed love and hate relationship doesn't seem serious since roddy sometimes stays in germany's house. And fem!prussia has one of the best designs. She looks so cool and badass.
Also a lot of people changed their mind on france once that particular episode in season 5 aired and got all angst with him. but even then, the hetalia hype kinda went down by then and a lot left the fandom for a lot of reasons.