what does 'Ya hoser!' mean, please?

Just to add to what helen wrote...

It's usually used in the sense of "loser". As in, "You're such a hoser, eh?" You gotta watch Strange Brew (it's an older movie, maybe 15 or so years old, and stars Bob & Doug MacKenzie), then you'll get the "hoser" thing. Or else you'll think Canadian comedians are a buncha loonies.