Boring tax stuff warning!

AB: Your information is still current regarding professional gambling income. Essentially, you'd have to be "carrying on a business" of gambling. One of the tests is whether a "systematic method" is used, but it also depends on how much time is spent on the activity and the amount of assets and income applied.

You're also basically correct about the tax credit, but it's a bit more complicated than your explanation. Not much point in going into it though.

Interestingly, under the US-Canada tax treaty, Canadians can offset their US gambling losses against any US gambling gains so that they only have to pay US tax on their net winnings. To my knowledge, no other country has this agreement with the US.