Adaptation Dye-Job: Has lighter blond hair with darker tips in manga artwork, but the anime gives him a uniform dark blond shade. His eyes also changed from being violet (or light blue) to a deep blue. Both changes make him look even more like America. Season 5 gives him back his violet eyes, and changes his hair color to a strawberry blond shade.
Goggles Do Nothing: Possibly justified? Canada was the aircraft manufacturing and flight training center for most of the British Empire in WW2 and his uniform is aviator-appropriate and seems to include a parachute. While America is clearly dressed as a fighter pilot, Canada is likely to be a bombardier or navigator.
Heavy Sleeper: Seems to be narcoleptic, as one of the webcomic strips has him speaking to someone else and then both fall asleep randomly. See his quote as well.
The Unfavorite: Canada has always been overshadowed by America ever since they were little. As soon as England seemed to be paying more attention to Canada, America came along and took his attention back.
In fact, poor Canada is usually treated as a non-entity - people either forget who he is or don't even notice him. (In one strip Russia spends a whole meeting sitting in his lap because he didn't notice that Canada was already sitting in the chair. Later Russia comments to Belarus on how comfortable his chair was.)
Covert Pervert: Turns out that she really likes butts. (Or at least coconuts shaped like butts.)
The Ditz: She has a few moments. So far, she seems to be the spaciest of all the female characters, especially in the Christmas events, where she has texted Finland just to ask how he would describe ants being all over the place and tries to play in the snow as if it were sand.
Seychelles: Ah, can I eat the fish? It's a fresh fish. [...] Or would a flying fish be better? Is it?
Fan Nickname: The fandom hasn't really settled on a human name for her the way it has for Taiwan or Netherlands, but "Leonie", "Michelle" and "Angelique" are the most common human names for her in fanworks.
Joshikousei: She's the star of Gakuen Hetalia, as already mentioned.
Large Ham: She tends to be a bit over-dramatic sometimes. Her reaction to being told that her place would be the honeymoon destination for Will and Kate is a good example of this.
New Transfer Student: In the Gakuen Hetalia game, France convinces her to join the World Academy. When she draws her national crest on the chalkboard, the other members of her Africa Class laugh so hard at how cheesy it is they need to be taken to the school infirmary.
Only Sane Man: Averted. In Gakuen Hetalia, Seychelles attempts to put a curse on England, only to have him reveal himself as a lover of black magic as he starts begging for her to teach him. This causes Seychelles to think on how strange everyone in World Academy W is, not realizing that she is in fact just as weird as everyone else.
Seychelles: I'll say my name and everything straight up when I prank call England. I'll pretend to talk about the TV instruction manual with him.
Sassy Black Woman: The more positive side of this trope. She occasionally says snarky things about her (at the time) boss England as well, and is said to have dumped France in Christmas. Look below as well.
Shorttank: Seems to be getting this treatment in a few sketches as of late.
The Slacker: Despite her energetictendencies, Seychelles is described as being sloppy and a bit lazy. This shows up during the Christmas events where she puts off cleaning and is portrayed as being very carefree.
Sempai Kohai: Implied to be the nature of their relationship, as Monaco refers to Seychelles with the suffix "-kun", something often used by seniors referring to their kohai. Fandom often portrays them in this sort of relationship, or Monaco as Seychelles' Cool Big Sis.
Tsundere: In Gakuen Hetalia, she's a Type B that goes from demure and polite to screaming or swearing as soon as England or France push her too far, either by being bossy (England) or by groping her (France).
In the original Gakuen Hetalia script, one of the "bad endings" (the one where she joins the Axis) drives it very straight to the point, as it finished with Seychelles screaming and swearing that she'll kill England the next time they meet.
To England (After he clamps a dog collar on her and declares her his colony): LIKE HELL I WILL YOU EYEBROW BASTAAARD!
Ambiguous Gender: He was considered this for a long time, due to his design being considered cutesy and him not having made any significant appearances to denote a gender (along with his chest and body being concealed by a sheep at times). Himaruya's initial answer was bordering Shrug of God, or coming off more like a tease:
Is New Zealand-san a man or a woman?
New Zealand: Which do you think I am?
There was also much debate over whether or not the usage of "seinen" in his manga profile indicated that he was unamibiguously male, or whether seinen was being used in a gender-neutral context. However, the Hetaween 2013 Event notes broke the ambiguity by outright referring to him as a man, and he also has a male seiyu in the anime.