Generally the answer is no. If you live in Canada, you do not need to pay any taxes on profits from online gambling on slots, casino, poker, blackjack etc. There are two exceptions:
1. if you’re going to earn interest on the winnings from online gambling (this must be legally declared that on a T5 form),
or
2. if a significant proportion of your income comes from online gambling. In which case the profits are sometimes labelled as income and taxed accordingly (e.g. in the case of a professional gambler).