Not sure if it has been mentioned in here, but the case against a quebec sports lottery bettor was interesting. Here is a post elsewhere I found on it:
Originally Posted by tiltymcfish0
To summarize for others interested,
These articles are about a sports bettor in Quebec, who made about 7mill over 5 years and won his case against Revenue Canada who were trying to tax him.
Getting taxed in Canada on gambling is all about proving that what you do is a business. In this case, they hired "helpers" to make the bets which we don't have to worry about playing poker, but they only worked about 10min a day (poker looks more like a business in time invested). Another advantage to this sports bettor is he was betting through a sports lottery. Lottery winnings is specifically stated to be 100% tax exempt by Revenue Canada. Ends up they won the case, but it seems to me that they got lucky with their judge as he seemed to have the stereotypical view of gambling. Judge said their betting was compulsive and bizarre, where in fact they had system which involved statistical analysis and a computer program to help find the good bets.
Another note is the 1 article mentioned Revenue Canada has lost 12 of 14 cases where they have tried to tax gambling as a business. The 2nd article mentions to the wins for RC. A horse bettor who had inside information, and a pool pro who bet on his own games.