Well for one snakehead isn't one fish it's a type of fish with all different needs sizes and requirements. But no mostly not illegal in Canada. Yet. Though some places have restrictions on some specifics ones I believe. A few Canadians including myself keep snakeheads. But no one can give you a straight answer unless you can tell is what kind of snakehead you are looking at
Right now in Canada owning any species of snakehead has been banned in the provinces of Quebec & Ontario, as of right now they are legal in all other provinces, British columbia is the only other province that i'm aware of working to ban them. Last time i looked into it the plan was to have the ban in BC in place by the end of the summer/early fall of this year. No changes planned for other provinces. So although it is not illegal YET but likely will be where you live before the new year.
The species your looking at is channa micropeltes , Since you couldn't identify it I recommend AGAINST owning it. Putting aside the fact tat it'll likely be illegal in your province in a couple months. This is not a beginner snakehead , they get VERY large and are vrey aggressive will need a huge tank/indoor pond with a monster filtration system and heaters to match. Something around 500gallons would work PH on the slightly acidic side, and warm temps and keep it alone it'll kill anything you try to put with it big or small. Not trying to sound like a jerk but it's one of those fish where if you don't know what it is your likely not ready to own one and care for it.
IMO 100$ is way over priced, can get one for 10-20$ as a juvie at most pet shop's, in a year or so it'll be as big as the one our looking at now and STILL GROWING. it's one of those fish that starts off cheap and later your lucky if you can give it away. There arn't that many people running tropical ponds around, and if they do they don't likely ant to dedicate it to one fish.
Why would this one be illegal in bc?
The northern one should be since it's lives in cold climates am survives the northern was cought in a lake in Burnaby bc