I mean, all TAKOYAKI that I have ate in Japan so far is shit, but I am not going to go out on a limb and say 'Canadian takoyaki is far better than Japanese'.
The main things that are different when it comes to sushi are,
- How people eat it
- The cost (duh)
- Different varieties available
In Japan, It is less likely to find such sushi types such as California rolls, New york rolls, Spider maki, Dynamite rolls, Crispy tuna, Spicy tuna and so on. These are western inventions and are not common in Japan (but can be found).
In Japan, sushi restaurants don't usually sell all the extras such as Tempura and udon noodles like most western restaurants do. In Western sushi restaurants it is usually a mix of other Japanese foods packed into one (and sometimes its a Japanese/Korean restaurant, or even worse, No-named-random-Asian-mix-invention restaurant where the dishes are all mixed origin and usually just labeled as 'asian food').
In Japan, its traditional to eat sushi with your hands (still practiced today in some traditional style restaurants or by some people), but in the west this is generally considered rude. Oppositely, In western countries it is fairly normal to pick up tempura and eat it with your hand (This is a no-no in Japan).
Another no-no in Japan is dipping UNAGI SUSHI or INARIZUSHI in soysauce. In western countries theres no rules or tradition as to how you eat your Japanese food. In Japan, items that already have sauce on it are not supposed to be dipped. Part of the reason is due to the fact that the sauce will mix with your soysauce (causing you to explode) and the other part is it is just not the way things are supposed to be done. These sushi are supposed to be eaten SONO MAMA そのまま (The way it is).
As for quality of fish, that really depends on where you go. Its ignorant for people to say that Japanese sushi is better, because in Japan (like other countries) they get their fish from all around (not just Japan) so its unlikely the person who is eating the fish even knows where it came from.
As for my Canadian experience, the larger cities will have the better sushi. Toronto has plenty of great sushi restaurants. I believe that the smaller cities (such as Sudbury, Ontario), have less access to good ingredients thus the sushi there usually